Revert "MM-27312 Allow uploading 10 files per post (#16235)" (#16908)

This reverts commit 8e2986e5ed.

scripts/mattermost-mysql-5.0.sql

@@ -626,7 +626,7 @@ CREATE TABLE `Posts` (
   `Props` text,
   `Hashtags` text,
   `Filenames` text,
-  `FileIds` varchar(300) DEFAULT NULL,
+  `FileIds` varchar(150) DEFAULT NULL,
   `HasReactions` tinyint(1) DEFAULT NULL,
   PRIMARY KEY (`Id`),
   KEY `idx_posts_update_at` (`UpdateAt`),

scripts/mattermost-postgresql-5.0.sql

@@ -398,7 +398,7 @@ CREATE TABLE public.posts (
     props character varying(8000),
     hashtags character varying(1000),
     filenames character varying(4000),
-    fileids character varying(300),
+    fileids character varying(150),
     hasreactions boolean
 );