Drop the old-style runtime-prefix handling in interpolate_path()

After deprecating this in v2.34.0 (released November 15th, 2021), it is
time to drop it. This reverts commit 28fdfd8 (mingw: deprecate
old-style runtime-prefix handling in interpolate_path(), 2015-12-11).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

path.c

@@ -746,12 +746,6 @@ char *interpolate_path(const char *path, int real_home)
 	if (skip_prefix(path, "%(prefix)/", &path))
 		return system_path(path);
 
-#ifdef __MINGW32__
-	if (path[0] == '/') {
-		warning(_("encountered old-style '%s' that should be '%%(prefix)/%s'"), path, path);
-		return system_path(path + 1);
-	}
-#endif
 	if (path[0] == '~') {
 		const char *first_slash = strchrnul(path, '/');
 		const char *username = path + 1;