[LLVM] Remove wrong DBG_VALUE instruction with one operand in AArch64 test case

Summary:
AArch64 test case llvm/test/CodeGen/AArch64/branch-target-enforcement.mir is checking for invalid  DBG_VALUE instruction with one operand(`DBG_VALUE $lr`). And this DBG_VALUE instruction is echoed from test case it self only.

Correct format of DBG_VALUE is given in below link:
https://llvm.org/docs/SourceLevelDebugging.html#variable-locations-in-instruction-selection-and-mir

Reviewers: dsanders, eli.friedman, jmorse, vsk

Reviewed By: dsanders

Subscribers: kristof.beyls, danielkiss, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78309