Drop unused, but confusing macro definition (phpGH-15541)

`PHP7DLLTS_EXPORTS` is not used throughout php-src, and it's unlikely
that it is used by any extension, especially since it still refers to
PHP 7.  The symbol had been introduced in 2014[1], but is not even used
in latest PHP-7.4; probably it was just supposed to be used, or part of
phpng.

[1] <php@fc734cf>

Since CI already ran for the PR, we can now [skip ci].

Author: cmb69

win32/build/confutils.js

@@ -3241,7 +3241,7 @@ function toolset_setup_common_cflags()
 	var envCFLAGS = WshShell.Environment("PROCESS").Item("CFLAGS");
 
 	// CFLAGS for building the PHP dll
-	DEFINE("CFLAGS_PHP", "/D _USRDLL /D PHP7DLLTS_EXPORTS /D PHP_EXPORTS \
+	DEFINE("CFLAGS_PHP", "/D _USRDLL /D PHP_EXPORTS \
 	/D LIBZEND_EXPORTS /D TSRM_EXPORTS /D SAPI_EXPORTS /D WINVER=" + WINVER);
 
 	DEFINE('CFLAGS_PHP_OBJ', '$(CFLAGS_PHP) $(STATIC_EXT_CFLAGS)');