testsuite: remove Wstrict-overflow related tests

The following testsuite PRs are related to the now obsolete
Wstrict-overflow option:

- Bug 36227 - [4.3 Regression] POINTER_PLUS folding introduces undefined
  overflow
- Bug 48022 - [4.6 Regression] -Wstrict-overflow warning on code that
  doesn't have overflows
- Bug 49705 - -Wstrict-overflow should not diagnose unevaluated
  expressions
- Bug 52904 - -Wstrict-overflow false alarm with bounded loop

They are exercising code that no longer exists, so remove all of them.
Two other tests (pr81592.c and pragma-diag-3.c) have Wstrict-overflow
checks that got removed.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr81592.c: Removed strict-overflow options.
	* gcc.dg/pragma-diag-3.c: Removed Wstrict-overflow option, along
	with a reference and tests for PR66098 ("[5 regression] #pragma
	diagnostic 'ignored' not fullyundone by pop for
	strict-overflow").
	* gcc.dg/pr36227.c: Removed.
	* gcc.dg/pr48022-1.c: Removed.
	* gcc.dg/pr48022-2.c: Removed.
	* gcc.dg/pr49705.c: Removed.
	* gcc.dg/pr52904.c: Removed.