build: merge TrackMemory (CURLDEBUG) into debug-enabled option

Drop separate `TrackMemory` (aka `CURLDEBUG`) debug feature.

After recent changes (thread-safety,
193cb00ce9, and updates leading up to
it), `TrackMemory` is unlikely to cause build or runtime issues.

To simplify builds and debug options, enable `TrackMemory`
unconditionally for debug-enabled (aka `DEBUGBUILD`) builds. Before
this patch, this was already the default, with an option to disable
it, or enable it in non-debug-enabled builds.

Note, in practice these two debug options already went hand in hand. It
was not possible to toggle them separately for a long time due to bugs,
before 59dc9f7e69 (2024-05-28) fixed it.

This patch also removes/deprecates separate knobs and feature flags for
`TrackMemory`:
- autotools: `--enable-curldebug`/`--disable-curldebug`
- cmake: `-DENABLE_CURLDEBUG=ON`/`OFF`
- C macro: `CURLDEBUG`
- libcurl: `CURL_VERSION_CURLDEBUG` symbol deprecated in favor
  of `CURL_VERSION_DEBUG`. They always return the same value after this
  patch.

Also:
- drop `TrackMemory` from `curl -V` output.
- rename internal `CURLDEBUG` macro to `CURL_MEMDEBUG` internally.
  To avoid confusion with `DEBUGBUILD`, but to keep guarding
  `TrackMemory`-related internals for readability.
- runtests: bind `TrackMemory` to debug feature. Keep it a separate
  test feature requirement, for clarity.
- CI: drop test builds for combinations of the two options.
- GHA/linux: no longer disable TrackMemory in the TSAN job.

Ref: https://github.com/curl/curl/pull/20328#issuecomment-3754528407

Closes #20331

CMakeLists.txt

@@ -253,15 +253,11 @@ option(ENABLE_DEBUG "Enable curl debug features (for developing curl itself)" OF
 if(ENABLE_DEBUG)
   message(WARNING "This curl build is Debug-enabled and insecure, do not use in production.")
 endif()
-option(ENABLE_CURLDEBUG "Enable TrackMemory debug feature" ${ENABLE_DEBUG})
 
 set(CURL_DEBUG_MACROS "")
 if(ENABLE_DEBUG)
   list(APPEND CURL_DEBUG_MACROS "DEBUGBUILD")
 endif()
-if(ENABLE_CURLDEBUG)
-  list(APPEND CURL_DEBUG_MACROS "CURLDEBUG")
-endif()
 
 option(CURL_CLANG_TIDY "Run the build through clang-tidy" OFF)
 if(CURL_CLANG_TIDY)
@@ -1260,10 +1256,10 @@ if(CURL_USE_GSSAPI)
 endif()
 
 # libbacktrace
-option(CURL_USE_LIBBACKTRACE "Use libbacktrace. Requires build with TrackMemory and DWARF debug information." OFF)
+option(CURL_USE_LIBBACKTRACE "Use libbacktrace. Requires debug-enabled build and DWARF debug information." OFF)
 if(CURL_USE_LIBBACKTRACE)
-  if(NOT ENABLE_CURLDEBUG)
-    message(FATAL_ERROR "libbacktrace requires TrackMemory enabled")
+  if(NOT ENABLE_DEBUG)
+    message(FATAL_ERROR "libbacktrace requires debug-enabled build for TrackMemory")
   endif()
   if(NOT CMAKE_BUILD_TYPE MATCHES "(Debug|RelWithDebInfo)")
     message(FATAL_ERROR "libbacktrace requires debug information")
@@ -1981,7 +1977,6 @@ curl_add_if("HTTPS-proxy"   NOT CURL_DISABLE_PROXY AND _ssl_enabled AND (USE_OPE
 curl_add_if("Unicode"       ENABLE_UNICODE)
 curl_add_if("threadsafe"    HAVE_ATOMIC OR (USE_THREADS_POSIX AND HAVE_PTHREAD_H) OR WIN32)
 curl_add_if("Debug"         ENABLE_DEBUG)
-curl_add_if("TrackMemory"   ENABLE_CURLDEBUG)
 curl_add_if("ECH"           _ssl_enabled AND HAVE_ECH)
 curl_add_if("HTTPSRR"       _ssl_enabled AND USE_HTTPSRR)
 curl_add_if("PSL"           USE_LIBPSL)