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

This reverts commit 8e2986e5ed.

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
 );