Remove cache from `ImageNode.get_filter`

This operations is incredibly efficient, and not often called.

wagtail/images/templatetags/wagtailimages_tags.py

@@ -1,5 +1,4 @@
 import re
-from functools import lru_cache
 
 from django import template
 from django.core.exceptions import ImproperlyConfigured
@@ -106,7 +105,6 @@ class ImageNode(template.Node):
         self.filter_specs = filter_specs
         self.preserve_svg = preserve_svg
 
-    @lru_cache
     def get_filter(self, preserve_svg=False):
         if preserve_svg:
             return Filter(to_svg_safe_spec(self.filter_specs))