Remove caching of filemask regexp

It's not used much often and the performance benefit is not visible.
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/subproject.py

@@ -395,15 +395,12 @@ class SubProject(models.Model, PercentMixin, URLMixin, PathMixin):
         self._all_flags = None
         self._linked_subproject = None
         self._repository = None
-        self._filemask_re = None
 
     @property
     def filemask_re(self):
-        if self._filemask_re is None:
-            self._filemask_re = re.compile(
-                fnmatch.translate(self.filemask).replace('.*', '(.*)')
-            )
-        return self._filemask_re
+        return re.compile(
+            fnmatch.translate(self.filemask).replace('.*', '(.*)')
+        )
 
     @property
     def log_prefix(self):