Avoid over-linking with GLib

This undos part of commit 2d273ec9.

glib.h is used in the public header, yes. However, that does not require the whole library, just its headers (please, correct me, if I am wrong). Furthermore, the crypto library NSS is already handled by ‘dependencies’ in ‘library’. Actually, when not both but just shared library is built in Meson, NSS is not listed in Require.private in the resulting .pc file anymore. That avoids ‘over-depend’ for the -dev package in Debian based systems, see …

This here fixes the build-system Meson. There is still a .pc.in file for the legacy build-system make. Shall I change that as well?