[lldb] Rename MemoryTagManager RemoveNonAddressBits to RemoveTagBits

This better describes the intent of the method. Which for AArch64
is removing the top byte which includes the memory tags.

It does not include pointer signatures, for those we need to use
the ABI plugin. The rename makes this a little more clear.

It's a bit awkward that the memory tag manager is removing the whole
top byte not just the memory tags but it's an improvement for now.

Reviewed By: omjavaid

Differential Revision: https://reviews.llvm.org/D117671