Revert "[IR]Add NumSrcElts param to is..Mask static function in ShuffleVectorInst."

This reverts commit 9f5960e004ff54082ccfa9396522e07358f5b66b to fix
buildbots reported here https://lab.llvm.org/buildbot/#/builders/230/builds/19412.

GitOrigin-RevId: ebcb5d59fc7d3a33f0239db883bae228639b0725
15 files changed