Revert r345009 "[DebugInfo] Generate debug information for labels. (After fix PR39094)"

This broke the Chromium build. See
https://bugs.chromium.org/p/chromium/issues/detail?id=898152#c1 for the
reproducer.

> Generate DILabel metadata and call llvm.dbg.label after label
> statement to associate the metadata with the label.
>
> After fixing PR37395.
> After fixing problems in LiveDebugVariables.
> After fixing NULL symbol problems in AddressPool when enabling
> split-dwarf-file.
> After fixing PR39094.
>
> Differential Revision: https://reviews.llvm.org/D45045

llvm-svn: 345026