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

Those calls cause the strings to be escaped twice : by db_prepare* and
then by db_query_bound, which leads to backslashes apparing in the
database.

All c_ prefixed variables have been removed as well, as there is no need
anymore for SQL cleaned variables.

Fixes 0014541

Signed-off-by: Damien Regad damien.regad@merckgroup.com