Fix: remove obsolete theme_id column

The theme_id column was removed in schema version 83 update script, but not in the initialization one.

schema/ttrss_schema_mysql.sql

@@ -44,7 +44,6 @@ create table ttrss_users (id integer primary key not null auto_increment,
 	pwd_hash varchar(250) not null,
 	last_login datetime default null,
 	access_level integer not null default 0,
-	theme_id integer default null,
 	email varchar(250) not null default '',
 	full_name varchar(250) not null default '',
 	email_digest bool not null default false,