schema_tables: Don't alter tables which differ only in version

We apply deletion of scylla_tables.version to the incoming schema
mutations so that table schema version is recalculated after merge.
The mutations which we read from local schema tables may not have it
deleted in which case all tables would be considered as differing on
the presence of the version field. Avoid this by deleting the field
from old mutations as well.

db/schema_tables.cc

@@ -801,6 +801,15 @@ static future<> do_merge_schema(distributed<service::storage_proxy>& proxy, std:
        /*auto& old_aggregates = */read_schema_for_keyspaces(proxy, AGGREGATES, keyspaces).get0();
 #endif
 
+       // Incoming mutations have the version field deleted. Delete here as well so that
+       // schemas which are otherwise equal don't appear as differing.
+       for (auto&& e : old_column_families) {
+           schema_mutations& sm = e.second;
+           if (sm.scylla_tables()) {
+               delete_schema_version(*sm.scylla_tables());
+           }
+       }
+
        proxy.local().mutate_locally(std::move(mutations)).get0();
 
        if (do_flush) {

schema_mutations.hh

@@ -69,6 +69,10 @@ public:
         return _scylla_tables;
     }
 
+    mutation_opt& scylla_tables() {
+        return _scylla_tables;
+    }
+
     const mutation_opt& indices_mutation() const {
         return _indices;
     }