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

lib/curl_setup.h

@@ -953,7 +953,11 @@ extern curl_calloc_callback Curl_ccalloc;
 
 #include <curl/curl.h> /* for CURL_EXTERN, curl_socket_t, mprintf.h */
 
-#ifdef CURLDEBUG
+#ifdef DEBUGBUILD
+#define CURL_MEMDEBUG
+#endif
+
+#ifdef CURL_MEMDEBUG
 #ifdef __clang__
 #  define ALLOC_FUNC         __attribute__((__malloc__))
 #  if __clang_major__ >= 4
@@ -1049,7 +1053,7 @@ CURL_EXTERN ALLOC_FUNC FILE *curl_dbg_fdopen(int filedes, const char *mode,
   curl_dbg_accept4(sock, addr, len, flags, __LINE__, __FILE__)
 #endif
 
-#else /* !CURLDEBUG */
+#else /* !CURL_MEMDEBUG */
 
 #define sclose(x) CURL_SCLOSE(x)
 #define fake_sclose(x) Curl_nop_stmt
@@ -1065,11 +1069,11 @@ CURL_EXTERN ALLOC_FUNC FILE *curl_dbg_fdopen(int filedes, const char *mode,
 #define CURL_ACCEPT4 accept4
 #endif
 
-#endif /* CURLDEBUG */
+#endif /* CURL_MEMDEBUG */
 
 /* Allocator macros */
 
-#ifdef CURLDEBUG
+#ifdef CURL_MEMDEBUG
 
 #define curlx_strdup(ptr)          curl_dbg_strdup(ptr, __LINE__, __FILE__)
 #define curlx_malloc(size)         curl_dbg_malloc(size, __LINE__, __FILE__)
@@ -1087,7 +1091,7 @@ CURL_EXTERN ALLOC_FUNC FILE *curl_dbg_fdopen(int filedes, const char *mode,
 #endif
 #endif /* _WIN32 */
 
-#else /* !CURLDEBUG */
+#else /* !CURL_MEMDEBUG */
 
 #ifdef BUILDING_LIBCURL
 #define curlx_strdup(ptr)          Curl_cstrdup(ptr)
@@ -1115,7 +1119,7 @@ CURL_EXTERN ALLOC_FUNC FILE *curl_dbg_fdopen(int filedes, const char *mode,
 #endif
 #endif /* _WIN32 */
 
-#endif /* CURLDEBUG */
+#endif /* CURL_MEMDEBUG */
 
 /* Some versions of the Android NDK is missing the declaration */
 #if defined(HAVE_GETPWUID_R) && \