[llvm] [Hexagon] Clean up the test from hexinsert pass fix (PR #164858)

[Alexey Karyakin via llvm-commits]

quic-akaryaki wrote:

Sorry for unnecessary churn. Adding the extra checks besides the MIR verification was a mistake. I manually verified that `-verify-machineinstrs` catches the error with the fix reverted.

https://github.com/llvm/llvm-project/pull/164858