[libunwind][PAuthLR] Remove PC offset when using FEAT_PAuthLR

When originally introduced to libunwind as part of llvm#112171,
FEAT_PAuthLR had its Call Frame Instruction's (CFI's) in a different
location to other Signing Authentication methods. To incorporate this
in libunwind, an offset was introduced to work with this. However,
this design was reversed in llvm#121551 so the CFI's are emitted in the
same location as other methods. When making this change, the offset
in libunwind was not removed, so libunwinds PC value would be incorrect.

This can be removed from the code, as it is no longer needed.

Author: Stylie777

libunwind/src/DwarfParser.hpp

@@ -808,12 +808,6 @@ bool CFI_Parser<A>::parseFDEInstructions(A &addressSpace,
             results->savedRegisters[UNW_AARCH64_RA_SIGN_STATE].value ^ 0x3;
         results->setRegisterValue(UNW_AARCH64_RA_SIGN_STATE, value,
                                   initialState);
-        // When calculating the value of the PC, it is assumed that the CFI
-        // instruction is placed before the signing instruction, however it is
-        // placed after. Because of this, we need to take into account the CFI
-        // instruction is one instruction call later than expected, and reduce
-        // the PC value by 4 bytes to compensate.
-        results->ptrAuthDiversifier = fdeInfo.pcStart + codeOffset - 0x4;
         _LIBUNWIND_TRACE_DWARF(
             "DW_CFA_AARCH64_negate_ra_state_with_pc(pc=0x%" PRIx64 ")\n",
             static_cast<uint64_t>(results->ptrAuthDiversifier));