[llvm] [SystemZ] Remove getInliningThresholdMultiplier() override (PR #94612)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

Thanks for the update. However, I have been working on tracking down the regressions I have seen (imagick, povray and perl), and have made some progress. I believe I will have a patch ready soon, which will set the multiplier to 1 and boost the threshold for specific types of callees.

https://github.com/llvm/llvm-project/pull/94612