Move groupNames mask definition to its user

Move groupNames mask definition to its user

groupNames was declared in compat.c as a global to anything which
included compat.h (for which groupNames was its sole reason to exist),
but only ever used in indicators.c.

Which is kind of fortunate, given that e314931e removed identical
definitions of groupNames (as integers, not masks) from both action.c
and symbols.c.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>