package/x11r7/libepoxy: bump to version 1.3.1

Removed call to pkgconf because epoxy configure now uses pkgconf
itself to find egl headers:
https://github.com/anholt/libepoxy/commit/d56f21c494b315306215c4730835a9b291360e9b



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>