Remove flushAndSubit from SkiaPipeline renderFrame.

Previously we would submit a command buffer for the
frames draws and then immediately submit a second
command buffer that had no commands and just an attached
semaphore. This merges those two submit calls into Skia
into one call.

Test: manual running of system of benches
Bug: 175913056

Change-Id: If0d054960de8b459814cbfa9289756f8ee9d4a93
(cherry picked from commit f16ba601)