simplify PdoAdapter fetch functions
simplify PdoAdapter fetch functions

The fetch function defines a temporary variable for no practical
purpose and fetchAll uses a while loop to collect all results
through fetch instead of just calling the native fetchAll
function.

Signed-off-by: Matthew Peveler <ceb7192332cc0210660ce4c985cae5ba0e431884@gmail.com>

robmorgan/phinx