* lang_php/parsing/conflicts.txt: clean
pfff: support for Pair

Test Plan:
unit test included
make test

Reviewers: pieter, julienv

Reviewed By: pieter

CC: andrewparoski, jdelong, platform-diffs@lists

Differential Revision: https://phabricator.fb.com/D829823
* lang_php/parsing/parser_php.mly: