Cleanup: remove unused temp directory initialization

This last worked in v2.27 (2003) where all paths were initialized to "/"
which was still checked to initialize the temp directory.

This hasn't been the case since 932e9e8316
where it changed to "/tmp/", then an empty string (current default).

source/blender/blenkernel/BKE_appdir.h

@@ -60,7 +60,6 @@ bool BKE_appdir_program_python_search(char *fullpath,
 
 /* Initialize path to temporary directory. */
 void BKE_tempdir_init(char *userdir);
-void BKE_tempdir_system_init(char *dir);
 
 const char *BKE_tempdir_base(void);
 const char *BKE_tempdir_session(void);

source/blender/blenkernel/intern/appdir.c

@@ -998,14 +998,6 @@ const char *BKE_tempdir_base(void)
   return btempdir_base;
 }
 
-/**
- * Path to the system temporary directory (with trailing slash)
- */
-void BKE_tempdir_system_init(char *dir)
-{
-  where_is_temp(dir, NULL, FILE_MAX, NULL);
-}
-
 /**
  * Delete content of this instance's temp dir.
  */

source/blender/windowmanager/intern/wm_files.c

@@ -415,9 +415,6 @@ static void wm_init_userdef(Main *bmain)
   MEM_CacheLimiter_set_maximum(((size_t)U.memcachelimit) * 1024 * 1024);
   BKE_sound_init(bmain);
 
-  if (STREQ(U.tempdir, "/")) {
-    BKE_tempdir_system_init(U.tempdir);
-  }
   /* Update `U.tempdir` from user preferences. */
   BKE_tempdir_init(U.tempdir);