[llvm-dev] [LLParser] Remove deplibs related defines and functions

[via llvm-dev]

> I tried this cleanup in 2020, but a point was raised that this can be
> used to read old bitcode files. See https://reviews.llvm.org/D73422 

D73422 removed both textual IR parsing and bitcode reading.  Textual IR
never really had any backward-compatibility guarantees.  The new patch
removes only textual IR parsing, it does not remove bitcode reading; it
should be fine to do this.
--paulr