Remove unused PTHREADS CPP macro definition (#14759)

Author: petk

TSRM/tsrm.m4

@@ -10,8 +10,6 @@ if test "$pthreads_working" != "yes"; then
   AC_MSG_ERROR(Your system seems to lack POSIX threads.)
 fi
 
-AC_DEFINE(PTHREADS, 1, Whether to use Pthreads)
-
 AC_MSG_CHECKING(for POSIX threads)
 AC_MSG_RESULT(yes)
 ])

UPGRADING.INTERNALS

@@ -137,6 +137,7 @@ PHP 8.4 INTERNALS UPGRADE NOTES
    - Symbol HAVE_LIBPQ has been removed.
    - Symbols HAVE_LIBRT and HAVE_TIMER_CREATE removed.
    - Symbols PHP_FPM_SYSTEMD, PHP_FPM_USER, and PHP_FPM_GROUP removed.
+   - Symbol PTHREADS has been removed.
    - M4 macro PHP_DEFINE (atomic includes) removed (use AC_DEFINE and config.h).
    - M4 macro PHP_WITH_SHARED has been removed (use PHP_ARG_WITH).
    - M4 macro PHP_STRUCT_FLOCK has been removed (use AC_CHECK_TYPES).