gitserver: Remove feature flag enableGitServerCommandExecFilter
Created by: indradhanush
We have noticed no regressions so it is safe to remove the flag and enable the guarded behaviour by default.
Closes #31388.
Closes the loop on https://github.com/sourcegraph/security-issues/issues/213.
Easier to see the diff with hide whitespace enabled.
Test plan
sg start dotcom
works locally. No additional testing required.
Post deployment
Remove the flag from site config on dogfood and cloud.