Revert "[clang] Merge lifetimebound and GSL code paths for lifetime analysis (llvm#104906)" (llvm#105752)

Revert as it breaks libc++ tests, see llvm#104906.

This reverts commit c368a72.

Author: vitalybuka

clang/docs/ReleaseNotes.rst

@@ -239,8 +239,6 @@ Improvements to Clang's diagnostics
 
 - Clang now diagnoses when the result of a [[nodiscard]] function is discarded after being cast in C. Fixes #GH104391.
 
-- Don't emit duplicated dangling diagnostics. (#GH93386).
-
 - Improved diagnostic when trying to befriend a concept. (#GH45182).
 
 Improvements to Clang's time-trace