Revert r343089 "[AArch64] - Return address signing dwarf support"

Revert r343089 "[AArch64] - Return address signing dwarf support"

This caused the DebugInfo/Sparc/gnu-window-save.ll test to fail.

> Functions that have signed return addresses need additional dwarf support:
> - After signing the LR, and before authenticating it, the LR register is in a
>   state the is unusable by a debugger or unwinder
> - To account for this a new directive, .cfi_negate_ra_state, is added
> - This directive says the signed state of the LR register has now changed,
>   i.e. unsigned -> signed or signed -> unsigned
> - This directive has the same CFA code as the SPARC directive GNU_window_save
>   (0x2d), adding a macro to account for multiply defined codes
> - This patch matches the gcc implementation of this support:
>   https://patchwork.ozlabs.org/patch/800271/
>
> Differential Revision: https://reviews.llvm.org/D50136

llvm-svn: 343103