Remove dependency on non-Treble OMX

This essentially reverts commit ba40190c,
which was made originally for b/69110957.

The change in addition to reverting is the reordering of calls in
main_codecservice.cpp. This CL makes the call to SetUpMinijail() come
before the call to ProcessState::self()->startThreadPool().

Test: make cts -j123 && cts-tradefed run cts-dev -m \
CtsMediaTestCases --compatibility:module-arg \
CtsMediaTestCases:include-annotation:\
android.platform.test.annotations.RequiresDevice

Test: make vts -j123 && vts-tradefed run commandAndExit vts \
--skip-all-system-status-check \
--skip-preconditions -m VtsHalMediaOmxV1_0Host \
-l INFO

Bug: 67990472
Change-Id: Ic62acf3ae1aa3f9249e5c3ce542fb4f95689704e