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

appveyor.yml

@@ -53,14 +53,13 @@ environment:
       PRJ_CFG: Release
       OPENSSL: 'ON'
       SHARED: 'ON'
-    - job_name: 'CM VS2022, Release, arm64, Schannel, Static, Build-tests'
+    - job_name: 'CM VS2022, Release, arm64, Schannel, Static, no-DEBUGBUILD, Build-tests'
       APPVEYOR_BUILD_WORKER_IMAGE: 'Visual Studio 2022'
       PRJ_GEN: 'Visual Studio 17 2022'
       TARGET: '-A ARM64'
       PRJ_CFG: Release
       SCHANNEL: 'ON'
       DEBUG: 'OFF'
-      CURLDEBUG: 'ON'
     - job_name: 'CM VS2010, Debug, x64, Schannel, Shared, Build-tests & examples'
       APPVEYOR_BUILD_WORKER_IMAGE: 'Visual Studio 2013'
       PRJ_GEN: 'Visual Studio 10 2010'
@@ -120,14 +119,7 @@ environment:
       ENABLE_UNICODE: 'ON'
       EXAMPLES: 'ON'
       TOOLSET: 'ClangCl'
-    - job_name: 'CM VS2022, Debug, x64, Schannel, Static, Unicode, Build-tests'
-      APPVEYOR_BUILD_WORKER_IMAGE: 'Visual Studio 2022'
-      PRJ_GEN: 'Visual Studio 17 2022'
-      TARGET: '-A x64'
-      PRJ_CFG: Debug
-      SCHANNEL: 'ON'
-      ENABLE_UNICODE: 'ON'
-    - job_name: 'CM VS2022, Release, x64, Schannel, Shared, Unicode, DEBUGBUILD, no-CURLDEBUG, Build-tests'
+    - job_name: 'CM VS2022, Release, x64, Schannel, Shared, Unicode, no-DEBUGBUILD, Build-tests'
       APPVEYOR_BUILD_WORKER_IMAGE: 'Visual Studio 2022'
       PRJ_GEN: 'Visual Studio 17 2022'
       TARGET: '-A x64'
@@ -135,7 +127,7 @@ environment:
       SCHANNEL: 'ON'
       ENABLE_UNICODE: 'ON'
       SHARED: 'ON'
-      CURLDEBUG: 'OFF'
+      DEBUG: 'OFF'
     - job_name: 'CM VS2022, Debug, x64, no SSL, Static, Build-tests'
       APPVEYOR_BUILD_WORKER_IMAGE: 'Visual Studio 2022'
       PRJ_GEN: 'Visual Studio 17 2022'