IOMX: remove allocateBufferWithBackup

Only keep useBuffer. Pass in quirks requirement for now, once
we have access to MediaCodecList XML info in OMX, we can remove
the quirks from IOMX.

Also remove a few unused variables on BufferMeta.

bug: 31399200
Change-Id: I93bef964ce034d4aeb1f5d13a75f130108e4e648