callrecording should locate php scripts via ${AMPBIN}

The callrecording module emits a couple of dialplan rules, that execute php
scripts.

Currently (well, module version 13.0.11), these scripts are found via:

FreePBX::Config()->get('ASTVARLIBDIR').'/bin/stoprecording.php

and

FreePBX::Config()->get('ASTVARLIBDIR').'/bin/one_touch_record.php

It would be superior to just execute them as:

${AMPBIN}/stoprecording.php

and

${AMPBIN}/one_touch_record.php

respectively.