examples: don't override LINK and other variables

Defining our own LINK causes us to run into some trouble with LDFLAGS,
which commit 16bb5c8075ae3d18fa3b19fdd1b479b4cf17a96b already
demonstrated.

LDFLAGS does need to be included here, but it's probably even easier to
just use the default value.

https://bugzilla.gnome.org/show_bug.cgi?id=724195