Remove extra wait in sceGnmSubmitDone (#5060)

Seems I accidentally misunderstood something I saw in my decomp of the submit done ioctl. This one change effectively made submits synchronous, which was good for local testing, but effectively a hack.
This will re-break a bunch of things who's PM4 type 0 issues were fixed by my submit fixes PR.

src/core/libraries/gnmdriver/gnmdriver.cpp

@@ -2361,7 +2361,6 @@ s32 PS4_SYSV_ABI sceGnmSubmitDone() {
         submission_lock = true;
     }
     liverpool->SubmitDone();
-    WaitGpuIdle();
     send_init_packet = true;
     ++frames_submitted;
     DebugState.IncGnmFrameNum();