xgettext: PHP: Revert recently introduced code duplication.
* gettext-tools/src/x-php.c (process_dquote_or_heredoc): New function, extracted
from process_heredoc.
(process_heredoc): Allocate a php_extractor on the stack. Invoke
process_dquote_or_heredoc.
(phase4_get): Invoke process_dquote_or_heredoc.
