Remove pushrebase_disable_rebased_commit_validation tunable

Summary: The pushrebase_disable_rebased_commit_validation tunable was added to guard a new set of validations that we put in place to address problems in pushrebasing diamond merge commits. However, its been more than 3 years since that logic was enabled in production and we never disabled it once. Makes sense to get rid of this check completely

Reviewed By: mzr

Differential Revision: D50261925

fbshipit-source-id: c2bdec2d27a83821b294a27d3a4249de76b3296f

eden/mononoke/pushrebase/src/lib.rs

@@ -107,7 +107,6 @@ use repo_identity::RepoIdentityRef;
 use slog::info;
 use stats::prelude::*;
 use thiserror::Error;
-use tunables::tunables;
 
 define_stats! {
     prefix = "mononoke.pushrebase";
@@ -483,13 +482,6 @@ async fn maybe_validate_commit(
     bcs_id: &ChangesetId,
     retry_num: PushrebaseRetryNum,
 ) -> Result<(), PushrebaseError> {
-    if tunables()
-        .pushrebase_disable_rebased_commit_validation()
-        .unwrap_or_default()
-    {
-        return Ok(());
-    }
-
     // Validation is expensive, so do it only once
     if !retry_num.is_first() {
         return Ok(());