Remove object-fit polyfill for the old Microsoft Edge (#22693)

* chore: remove object-fit-images and its postcss packages

* chore: update postcss config

* chore: remove object-fit-image from extra_polyfills.js

* chore: remove object-fit property check from load_polyfills.js

app/javascript/mastodon/extra_polyfills.js

@@ -1,6 +1,3 @@
 import 'abortcontroller-polyfill/dist/abortcontroller-polyfill-only';
 import 'intersection-observer';
 import 'requestidlecallback';
-import objectFitImages from 'object-fit-images';
-
-objectFitImages();