multibuild.eclass: Revert "Reap stray subjobs before exiting sub-phase"

The code wrongly relies on 'bash -n' which is not available in bash 4.2.

Bug: https://bugs.gentoo.org/615642
Reverts: e5e4a35151

eclass/multibuild.eclass

@@ -125,18 +125,6 @@ multibuild_foreach_variant() {
 		_multibuild_run "${@}" \
 			> >(exec tee -a "${T}/build-${MULTIBUILD_ID}.log") 2>&1
 		lret=${?}
-
-		# make sure no processes are left over
-		local leftovers=
-		while :; do
-			wait -n
-			[[ ${?} -eq 127 ]] && break || leftovers=1
-		done
-
-		if [[ ${leftovers} ]]; then
-			ewarn "The multibuild function has left one or more processes running"
-			ewarn "in the background. Please report a bug."
-		fi
 	done
 	[[ ${ret} -eq 0 && ${lret} -ne 0 ]] && ret=${lret}