g_malloc(), etc, never return NULL, by API contract. Likewise, by
extension, no other glib function ever returns NULL due to lack of
memory. So remove lots of unnecessary checks (the vast majority of
which would have immediately crashed had they ever run anyway, since
g_set_error(), g_warning(), and nm_log_*() all need to allocate
memory).

https://bugzilla.gnome.org/show_bug.cgi?id=693678