Delete framebuffers on format change

[unknownbrackets]

This fixes #2758 and seems likely to fix other games mentioned there too.

The only dangerous thing is it might churn if the game uses the same memory as two types of framebuffers over and over.

-[Unknown]

[unknownbrackets]

As mentioned in the issue, I thought of another method, might be good in addition / if this causes problems. Could scan fbCache_ in DetachFramebuffer(). That's probably why this change helps.

But I'm not sure there's a reason to maintain the wrong format fb anyway?

-[Unknown]

[unknownbrackets]

I guess deleting doesn't work for all games, for some reason, but it should be dangerous to keep the old framebuffer's size.

-[Unknown]

[hrydgard]

There might actually be reasons to retain it, but only if scissor rect or something is set so that they don't actually overlap I guess. would still be kinda strange.

[Blutgang]

This pull request seems to break Dissidia 012 Duodecim Final Fantasy and Kingdom Hearts Birth By Sleep FM in Non-buffered rendering mode. (Black screen during battle as well as black cutscenes...the subtitles still show though)

[unknownbrackets]

See #3664.

-[Unknown]