sys-devel/gcc: 7.4.0: drop unappliable 23_all-pgo.patch

sys-devel/gcc: 7.4.0: drop unappliable 23_all-pgo.patch

23_all-pgo.patch used not to apply due to mis-named patch.

commit bd758f25a8246 ("toolchain.eclass: isolate 'epatch'
into 'tc_apply_patches'") started applying all patches
unconditionall and exposed the problem.

The change reverts back to previous patches (misses exactly
that patch).

Reported-by: Samuel Bernardo
Closes: https://bugs.gentoo.org/698130
Package-Manager: Portage-2.3.76, Repoman-2.3.17
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>