gpu: Remove unused extra_data_field from sync token.

This was used for storing the stream id on the client to flush the
correct stream. But, since cross-stream multi-flush was implemented, it
hasn't been used.

R=piman
BUG=NONE

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I5c161bbcf5ea763e30e4c148fc0c41729d6e7840
Reviewed-on: https://chromium-review.googlesource.com/825958
Reviewed-by: Martin Barbella <[email protected]>
Reviewed-by: Dale Curtis <[email protected]>
Reviewed-by: Kenneth Russell <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Antoine Labour <[email protected]>
Commit-Queue: Sunny Sachanandani <[email protected]>
Cr-Commit-Position: refs/heads/master@{#525497}
35 files changed