modules/common/Manifest.py: remove gc_dual_clock_ram, it's no more in the repo

modules/common/Manifest.py

@@ -10,7 +10,6 @@ files = [	"gencores_pkg.vhd",
                 "gc_arbitrated_mux.vhd",
                 "gc_pulse_synchronizer.vhd",
                 "gc_frequency_meter.vhd",
-                "gc_dual_clock_ram.vhd",
                 "gc_wfifo.vhd",
                 "gc_rr_arbiter.vhd",
                 "gc_prio_encoder.vhd",