GitLab: Remove "tags" stanzas

Given the structure of our current GitLab tests, we don't make real use
of the tags.  Furthermore, these tags prevent the automatic usage of the
default GitLab runners.  Remove these tags.

Reported-by: Roger Meier <r.meier@siemens.com>
Signed-off-by: Tom Rini <trini@konsulko.com>