Revert "[CGBlocks] Improve line info in backtraces containing *_helper_block"

Block copy/destroy helpers are now linkonce_odr functions, meant to be uniqued, and thus attaching debug information from one translation unit (or even just from one instance of many inside one translation unit) would be misleading and wrong in the general case.

This effectively reverts commit 9c6b6826.

<rdar://problem/59137040>

Differential Revision: https://reviews.llvm.org/D75615