[xulrunner] Use the system NSS CA trust library instead of the bundled copy

With the addition of p11-kit, we want to unify the CA trust stores
across the platform. p11-kit integrates with NSS by replacing
libnssckbi, the CA trust library, with a binary compatible version that
accesses the p11-kit store.

This is implemented in the system-wide nss and p11-kit packages by replacing a
subpackage that contains this library. For this browser version, so long
as we can rely on the ABI being compatible between browser nss, system nss,
and p11-kit, we can simply symlink to the system library and get the
same results.
[xulrunner] Remove add-sailfishos-org-certs.patch

These CAs are used only for internal software update servers. They
should not be in the system or browser trust stores. Also, this patch
has no effect after the previous commit which uses the system trust library
instead.