c++: don't remove labels during coro-early-expand-ifns [PR105104]

c++: don't remove labels during coro-early-expand-ifns [PR105104]

In some scenarios, it is possible for the CFG cleanup to cause one of
the labels mentioned in CO_YIELD, which coro-early-expand-ifns intends
to remove, to become part of some statement.  As a result, when that
label is removed, the statement it became part of becomes invalid,
crashing the compiler.

There doesn't appear to be a reason to remove the labels (anymore, at
least), so let's not do that.

	PR c++/105104

gcc/ChangeLog:

	* coroutine-passes.cc (execute_early_expand_coro_ifns): Don't
	remove any labels.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/torture/pr105104.C: New test.