cmake: minor improvements to cmake_uninstall.in.cmake

- reduce log noise by showing 'Uninstalling' message only if the file
  exists. (and a different message otherwise)
- replace cmake `rm` command with `file(REMOVE)`. For efficiency.
  Show manual message if the file could not be deleted.
  Ref: https://cmake.org/cmake/help/v3.18/command/file.html#remove
  Follow-up to 6d008352c6 #22193
- reduce log noise by showing 'Uninstalled' only if the deletion was
  successful. (and a different message otherwise)
- display `DESTDIR` env value if set.
- drop checking, setting and showing `CMAKE_INSTALL_PREFIX`.
  The value was never predefined, also not used, besides showing it,
  and showing it is misleading because `--prefix` may override the
  configure-time value, and also superfluous because the filenames
  are showing the actual prefix anyway.

Follow-up to 27e2a4733c

Closes #22201

CMake/cmake_uninstall.in.cmake

@@ -26,18 +26,22 @@ if(NOT EXISTS "${_manifest}")
   message(FATAL_ERROR "Cannot find install manifest: ${_manifest}")
 endif()
 
-if(NOT DEFINED CMAKE_INSTALL_PREFIX)
-  set(CMAKE_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@")
+set(_destdir "$ENV{DESTDIR}")
+if(NOT _destdir STREQUAL "")
+  message(STATUS "DESTDIR environment: ${_destdir}")
 endif()
-message(${CMAKE_INSTALL_PREFIX})
 
 file(READ "${_manifest}" _files)
 string(REGEX REPLACE "\n" ";" _files "${_files}")
 foreach(_file IN LISTS _files)
-  set(_target "$ENV{DESTDIR}${_file}")
-  message(STATUS "Uninstalling ${_target}")
+  set(_target "${_destdir}${_file}")
   if(IS_SYMLINK "${_target}" OR EXISTS "${_target}")
-    execute_process(COMMAND "@CMAKE_COMMAND@" -E rm -f -- "${_target}")
+    file(REMOVE "${_target}")
+    if(IS_SYMLINK "${_target}" OR EXISTS "${_target}")
+      message(STATUS "Failed to delete: ${_target}")
+    else()
+      message(STATUS "Uninstalled: ${_target}")
+    endif()
   else()
     message(STATUS "File does not exist: ${_target}")
   endif()

CMakeLists.txt

@@ -2452,9 +2452,7 @@ if(NOT CURL_DISABLE_INSTALL)
     DESTINATION ${_install_cmake_dir})
 
   if(NOT TARGET curl_uninstall)
-    # Consumed variables:
-    #   CMAKE_COMMAND
-    #   CMAKE_INSTALL_PREFIX
+    # Consumed variable:
     #   PROJECT_BINARY_DIR
     configure_file(
       "${PROJECT_SOURCE_DIR}/CMake/cmake_uninstall.in.cmake"