gcal is a leaf package, and the only one kept at gnu/packages/gcal.scm.
There is no special reason to keep it in a dedicated file.
* gnu/local.mk: Remove reference to packages/gcal.scm.
* gnu/packages/gcal.scm (gcal): Move from here ...
* gnu/packages/calendar.scm: ... to here.
Update copyright headers via merge.
* po/packages/POTFILES.in: Remove reference to gnu/packages/gcal.scm.
Change-Id: I196ce61ebb4caa683b97483f6ea1d6e505f05af7
Signed-off-by: Ludovic Courtès <ludo@gnu.org>