s/Get(Master|Replica)X/Get\1/g (#29520)

Drop the legacy `X` suffix from `GetMasterX` and `GetReplicaX`. The
presence of the suffix suggests there's a `non-X` version: but in fact
we migrated these away a long time ago, so remove the cognitive
overhead.

As an aside, this additionally helps avoid trip up LLMs that interpret
this as "something to fix".

server/channels/app/post_test.go

@@ -982,7 +982,7 @@ func TestCreatePost(t *testing.T) {
 		sqlStore := th.GetSqlStore()
 		sql := fmt.Sprintf("select count(*) from Posts where Id = '%[1]s' or OriginalId = '%[1]s';", previewPost.Id)
 		var val int64
-		err2 := sqlStore.GetMasterX().Get(&val, sql)
+		err2 := sqlStore.GetMaster().Get(&val, sql)
 		require.NoError(t, err2)
 
 		require.EqualValues(t, int64(1), val)