[opt] Remove the BreakpointPrinter pass

This removed the option print-breakpoints-for-testing in opt, as well
as the related BreakpointPrinter pass.

The functionality only existed for the legacy PM, but was not verified
to be working by any test cases. And the named "llvm.dbg.sp" metadata
that the pass was looking for is not something that I really can find
any information about (unless perhaps if I dive really deep into the
commit history), so not sure exactly if this functionality has been
relevant for several years.

Differential Revision: https://reviews.llvm.org/D148080