Revert of Convert enable_pre_sync_backup flag to new flags system. (patchset #4 id:60001 of https://codereview.chromium.org/1478623004/ )

Reason for revert:
Busted iOS http://build.chromium.org/p/chromium.mac/builders/iOS_Device/builds/30182/steps/compile/logs/stdio

Original issue's description:
> Convert enable_pre_sync_backup flag to new flags system.
>
> This flag's usage is very isolated so is a good candidate for the new system. There is now a generated header for the #define rather than a global define.
>
> Committed: https://crrev.com/bc4bccdacc16ccdf314870049033e03c463e478e
> Cr-Commit-Position: refs/heads/master@{#362284}

TBR=zea@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1485933002

Cr-Commit-Position: refs/heads/master@{#362297}
13 files changed