[CodeExtractor] Erase use-without-def debug intrinsics in parent func

[CodeExtractor] Erase use-without-def debug intrinsics in parent func

When CodeExtractor moves instructions to a new function, debug
intrinsics referring to those instructions within the parent function
become invalid.

This results in the same verifier failure which motivated r344545, about
function-local metadata being used in the wrong function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346255 91177308-0d34-0410-b5e6-96231b3b80d8