clean up GN targets that are already migrated, add pepper_hash_for_uma.

clean up GN targets that are already migrated, add pepper_hash_for_uma.

This updates the gn_all and gyp_remaining targets to reflect the current
status.

R=tfarina@chromium.org, brettw@chromium.org
BUG=461019
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:android_chromium_gn_compile_dbg,android_chromium_gn_compile_rel;tryserver.chromium.win:win8_chromium_gn_rel,win8_chromium_gn_dbg;tryserver.chromium.mac:mac_chromium_gn_rel,mac_chromium_gn_dbg

Review URL: https://codereview.chromium.org/1040543002

Cr-Commit-Position: refs/heads/master@{#322654}