Wrapper around the gpgme library Formula was removed
Last version was
php56-gnupg requires the following formulae to be installed:
autoconf 2.69 Automatic configure script builder
gpgme 1.11.1 Library access to GnuPG

Recent formula history

ilovezfs php56: migrate to homebrew/core (#4835)
Etienne Lachance Add PHP gnupg extension

Formula code at GitHub