[lensoverlay] Remove latency flag from CSB field trial config

The behaviour that the latency flag enabled is now triggered by default
when the CSB feature flag is enabled, so we can remove it.

Bug: 373878302
Change-Id: Ie129a3dee90e44fe2c45cc18130d1e77cd5633c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6064008
Reviewed-by: Duncan Mercer <mercerd@google.com>
Reviewed-by: Ali Stanfield <stanfield@google.com>
Commit-Queue: Jason Hu <hujasonx@google.com>
Cr-Commit-Position: refs/heads/main@{#1391205}