Improve SSH access

Just a minor pair of tweaks to postmarketos-ui-phosh and postmarketos-ui-phosh-qt_tweaks to prevent ssh sessions from trying to use wayland, which isn't remotable.

/etc/profile.d/gtk-app-wayland.sh:

#!/bin/sh

# Most pure GTK3 apps use wayland by default, but some,
# like Firefox, need the backend to be explicitely selected.
if [ "${SSH_CLIENT}" = "" ] ; then
export GDK_BACKEND=wayland
fi

/etc/profile.d/phosh-qt-tweaks.sh:

#!/bin/sh
if [ "${SSH_CLIENT}" = "" ] ; then
export QT_WAYLAND_DISABLE_WINDOWDECORATION=1
export QT_QPA_PLATFORM=wayland
fi