test-coffee: Fix the garbage collection test
test-coffee: Fix the garbage collection test

This test could sometimes fail because of a lack of free contiguous
pages in the file system. Fix this by removing the created files at the
end of each test. Besides, the test files do not have to be removed at
the beginning of each test since the file system is initially formatted.

Signed-off-by: Benoît Thébaudeau <b3efeb72fa9d3102885911404c5fbece843f6c8f@gmail.com>

MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki