[ticket/11040] search subject and text together
Instead of searching for post_subject and post_text seperately and then
OR them in where clause we use concatenation of the two columns and search

PHPBB3-11040
[ticket/11040] add post_content index

In addition to post_subject and post_title indexes add a post_content
which is concatenation of both the columns.

PHPBB3-11040
[ticket/11040] Remove postgres extra indexes
Remove separate indexes for post text and post subject and use
post content index which is sufficient

PHPBB3-11040