rtmp: drop support

- librtmp has no test cases, makes no proper releases and has not had a
  single commit within the last year

- librtmp parses the URL itself and requires non-compliant URLs for this

- we have no RTMP tests

- RTMP was used by 2.2% of curl users (self-identified in the 2025
  survey)

Closes #20673

CMake/FindLibrtmp.cmake

@@ -1,106 +0,0 @@
-#***************************************************************************
-#                                  _   _ ____  _
-#  Project                     ___| | | |  _ \| |
-#                             / __| | | | |_) | |
-#                            | (__| |_| |  _ <| |___
-#                             \___|\___/|_| \_\_____|
-#
-# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
-#
-# This software is licensed as described in the file COPYING, which
-# you should have received as part of this distribution. The terms
-# are also available at https://curl.se/docs/copyright.html.
-#
-# You may opt to use, copy, modify, merge, publish, distribute and/or sell
-# copies of the Software, and permit persons to whom the Software is
-# furnished to do so, under the terms of the COPYING file.
-#
-# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
-# KIND, either express or implied.
-#
-# SPDX-License-Identifier: curl
-#
-###########################################################################
-# Find the librtmp library
-#
-# Input variables:
-#
-# - `LIBRTMP_INCLUDE_DIR`:  Absolute path to librtmp include directory.
-# - `LIBRTMP_LIBRARY`:      Absolute path to `librtmp` library.
-#
-# Defines:
-#
-# - `LIBRTMP_FOUND`:        System has librtmp.
-# - `LIBRTMP_VERSION`:      Version of librtmp.
-# - `CURL::librtmp`:        librtmp library target.
-
-set(_librtmp_pc_requires "librtmp")
-
-if(CURL_USE_PKGCONFIG AND
-   NOT DEFINED LIBRTMP_INCLUDE_DIR AND
-   NOT DEFINED LIBRTMP_LIBRARY)
-  find_package(PkgConfig QUIET)
-  pkg_check_modules(_librtmp ${_librtmp_pc_requires})
-endif()
-
-if(_librtmp_FOUND AND _librtmp_INCLUDE_DIRS)
-  set(Librtmp_FOUND TRUE)
-  set(LIBRTMP_FOUND TRUE)
-  set(LIBRTMP_VERSION ${_librtmp_VERSION})
-  message(STATUS "Found Librtmp (via pkg-config): ${_librtmp_INCLUDE_DIRS} (found version \"${LIBRTMP_VERSION}\")")
-else()
-  find_path(LIBRTMP_INCLUDE_DIR NAMES "librtmp/rtmp.h")
-  find_library(LIBRTMP_LIBRARY NAMES "rtmp")
-
-  unset(LIBRTMP_VERSION CACHE)
-  if(LIBRTMP_INCLUDE_DIR AND EXISTS "${LIBRTMP_INCLUDE_DIR}/librtmp/rtmp.h")
-    set(_version_regex "#[\t ]*define[\t ]+RTMP_LIB_VERSION[\t ]+0x([0-9a-fA-F][0-9a-fA-F])([0-9a-fA-F][0-9a-fA-F]).*")
-    file(STRINGS "${LIBRTMP_INCLUDE_DIR}/librtmp/rtmp.h" _version_str REGEX "${_version_regex}")
-    string(REGEX REPLACE "${_version_regex}" "\\1" _version_str1 "${_version_str}")
-    string(REGEX REPLACE "${_version_regex}" "\\2" _version_str2 "${_version_str}")
-    math(EXPR _version_str1 "0x${_version_str1}" OUTPUT_FORMAT DECIMAL)
-    math(EXPR _version_str2 "0x${_version_str2}" OUTPUT_FORMAT DECIMAL)
-    set(LIBRTMP_VERSION "${_version_str1}.${_version_str2}")
-    unset(_version_regex)
-    unset(_version_str1)
-    unset(_version_str2)
-  endif()
-
-  include(FindPackageHandleStandardArgs)
-  find_package_handle_standard_args(Librtmp
-    REQUIRED_VARS
-      LIBRTMP_INCLUDE_DIR
-      LIBRTMP_LIBRARY
-    VERSION_VAR
-      LIBRTMP_VERSION
-  )
-
-  if(LIBRTMP_FOUND)
-    set(_librtmp_INCLUDE_DIRS ${LIBRTMP_INCLUDE_DIR})
-    set(_librtmp_LIBRARIES    ${LIBRTMP_LIBRARY})
-  endif()
-
-  mark_as_advanced(LIBRTMP_INCLUDE_DIR LIBRTMP_LIBRARY)
-
-  # Necessary when linking a static librtmp
-  find_package(OpenSSL)
-  if(OpenSSL_FOUND)
-    list(APPEND _librtmp_LIBRARIES OpenSSL::SSL OpenSSL::Crypto)
-  endif()
-endif()
-
-if(LIBRTMP_FOUND)
-  if(WIN32)
-    list(APPEND _librtmp_LIBRARIES "winmm")
-  endif()
-
-  if(NOT TARGET CURL::librtmp)
-    add_library(CURL::librtmp INTERFACE IMPORTED)
-    set_target_properties(CURL::librtmp PROPERTIES
-      INTERFACE_LIBCURL_PC_MODULES "${_librtmp_pc_requires}"
-      INTERFACE_COMPILE_OPTIONS "${_librtmp_CFLAGS}"
-      INTERFACE_INCLUDE_DIRECTORIES "${_librtmp_INCLUDE_DIRS}"
-      INTERFACE_LINK_DIRECTORIES "${_librtmp_LIBRARY_DIRS}"
-      INTERFACE_LINK_LIBRARIES "${_librtmp_LIBRARIES}")
-  endif()
-endif()

CMake/curl-config.in.cmake

@@ -91,10 +91,6 @@ if("@USE_LIBPSL@")
   find_dependency(Libpsl MODULE)
   list(APPEND _curl_libs CURL::libpsl)
 endif()
-if("@USE_LIBRTMP@")
-  find_dependency(Librtmp MODULE)
-  list(APPEND _curl_libs CURL::librtmp)
-endif()
 if("@USE_LIBSSH@")
   find_dependency(Libssh MODULE)
   list(APPEND _curl_libs CURL::libssh)