gdb.base/foll-fork.exp: remove DUPLICATEs

Remove DUPLICATEs, and and at the same time replace two uses of
gdb_test_multiple with gdb_test.  I don't think using gdb_test_multiple
is necessary here.

Change-Id: I8dcf097c3364e92d4f0e11f0c0f05dbb88e86742
1 file changed