Revert making Raw{Buffer,Image}::bind_memory unsafe

[marc0246]

This reverts the making unsafe of the bind_memory methods that was done in #2413, as it's a bit silly to make code that was safe before unsafe because of a niche use case which already comes with unsafe code.

Changelog:
Remove these lines:

### Breaking changes
Changes to buffers:
- `RawBuffer::bind_memory` is now marked unsafe.

Changes to images:
- `RawImage::bind_memory` is now marked unsafe.