Remove setup check for always_populate_raw_post_data
Summary:
rP23a49eb4 and rP7d8c84a7 bumped the required PHP version from 5.2.3 to 7.2.25.
Thus the check for `always_populate_raw_post_data` is unneeded now.
See also https://www.php.net/manual/en/migration56.deprecated.php
Test Plan: Unknown.
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26288