Remove all calls to the deprecated functions db_prepare* in "Docs" update page.

The aim of this change is to remove all calls to the deprecated functions db_prepare* in "Docs" update page.

Those calls caused the strings to be escaped twice : by db_prepare* and then by db_query_bound. 

This led to slashes apparing in the database.
I also removed all c_ prefixed variables, as there is no more SQL cleaned variables.