[FIX] website_{quote,sale}: payment tx handling consistency

Both website_sale and website_quote have logic to independently
confirm sales orders when a successful payment transaction is
processed.
Rev 46c5f93b introduced an extra
check and logging for transactions with mismatching amounts in
website_sale, but the same change was not done in website_quote.

Consequently, when both modules were installed, the tx mismatch
check was bypassed by website_quote, and a spurious logging message
was emitted by website_sale if the website_quote logic had executed
first.

This patch makes tx handling consistent in both modules, and avoids
the misleading log message when both modules are installed.