gst1-plugins-base: add missing indirect dependency on atomics for pango

Also removed the redundant indirect dependencies on wchar, threads, mmu
(gstreamer depends on libglib2 so this indirect dependency is obvious).

[Peter: drop wchar+threads from comment as suggested by Jerzy Grzegorek]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>