Trac #9493: Remove extra baggage from the ECL spkg

Remove GMP subdir.

Use tarball at:
* http://boxen.math.washington.edu/home/jpflori/upstream/ecl-12.12.1.201
40409.tar.bz2

URL: http://trac.sagemath.org/9493
Reported by: leif
Ticket author(s): Leif Leonhardy, Jean-Pierre Flori
Reviewer(s): Peter Bruin