[FuncSpec] Invalidate analyses when deleting a fully specialised function

Deleting a fully specialised function left dangling pointers in
`FunctionAnalysisManager`, which causes an internal compiler error
when the function's storage was reused.

Fixes bug #58759.

Reviewed By: ChuanqiXu

Differential Revision: https://reviews.llvm.org/D138909

Change-Id: Ifed378c748af35e8fe7dcbdddb0f41b8777cbe87