[lldb][NFC] Remove misleading ModulePass base class for IRForTarget
IRForTarget is never used by a pass manager or any other interface that requires
this class to inherit from Pass.
Also IRForTarget doesn't implement the current interface correctly because it
uses the runOnModule return value to indicate success/failure instead of
changed/not-changed, so if this ever ends up being used as a pass it would most
likely not work as intended.
Reviewed By: JDevlieghere
Differential Revision: https://reviews.llvm.org/D102677