Remove build-gdk-image, e2e:test-on-gdk, and retag-gdk-image jobs for stable branches

We want to remove these jobs from the stable branches, since GDK is not tested on these releases. The Docker images the jobs depend on get cleaned up before the stable branch expires

stable branch MR Handled By
16-4-stable-ee !158699 (merged) @nao.hashizume
16-6-stable-ee !160099 (merged) @stanhu
16-8-stable-ee !160102 (merged) @stanhu
16-9-stable-ee !160103 (merged) @stanhu
16-11-stable-ee !160107 (merged) @atevans
17-0-stable-ee !160111 (merged) @atevans
17-1-stable-ee !160128 (merged) @atevans
17-2-stable-ee !160129 (merged) @atevans
Edited by Andrew Evans