[llvm] [MC] Remove unused `MCAsmBackend::isMicroMips()` method (NFC) (PR #135581)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

FWIW on my downstream target I overload `MCStreamer::emitLabel()` for debug labels (introduce `MCStreamer::emitDebugLabel()`).
The reason is that on my target code labels must be 64-bit aligned (control transfer instructions require the destination to be aligned on that boundary). I need a separate method for debug labels because they must not be aligned, and it is impossible to differentiate them from code labels in `emitLabel()`. Debug labels must not be aligned because they may appear in a delay slot of a control transfer instruction, and aligning them will push a delayed instruction out of the delay slot.
I wonder if this approach could be useful for MIPS16.


https://github.com/llvm/llvm-project/pull/135581