This was causing large allocations in heap: https://github.com/turt2live/matrix-media-repo/issues/445

See https://github.com/matrix-org/matrix-spec-proposals/pull/2448/files#r1316159044

This reverts commit 9ee13765.

Fixes https://github.com/turt2live/matrix-media-repo/issues/340

Fixes https://github.com/turt2live/matrix-media-repo/issues/444

Also fixes a memory issue where we'd decode the entire image before deciding that the image is too small for thumbnailing.

see 1168a7f6

https://github.com/matrix-org/matrix-spec-proposals/pull/4034