Remove legacy .avifs extension mapping

The separate `image/avif-sequence` MIME type was removed [1]. This
patch updates our mappings accordingly.

[1]: AOMediaCodec/av1-avif#86

Bug: chromium:1207353
Change-Id: I3879b7f470693574998383a5a9bd0559d155e146
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/4285221
Commit-Queue: Ergün Erdoğmuş 
Auto-Submit: Mathias Bynens 
Reviewed-by: Ergün Erdoğmuş 

Author: mathiasbynens

front_end/core/common/ResourceType.ts

@@ -411,7 +411,6 @@ export const resourceTypeByExtension = new Map([
   ['xsl', resourceTypes.Stylesheet],
 
   ['avif', resourceTypes.Image],
-  ['avifs', resourceTypes.Image],
   ['bmp', resourceTypes.Image],
   ['gif', resourceTypes.Image],
   ['ico', resourceTypes.Image],
@@ -536,7 +535,6 @@ export const mimeTypeByExtension = new Map([
 
   // Image
   ['avif', 'image/avif'],
-  ['avifs', 'image/avif-sequence'],
   ['bmp', 'image/bmp'],
   ['gif', 'image/gif'],
   ['ico', 'image/ico'],