tc35815: Kill unused code

- TC35815_DMA_SYNC_ONDEMAND is always enabled.
- WORKAROUND_LOSTCAR is always enabled.
- WORKAROUND_100HALF_PROMISC is always enabled.
- GATHER_TXINT is always enabled.
- TC35815_USE_PACKEDBUFFER is always disabled.
- NO_CHECK_CARRIER is always disabled.

Signed-off-by: David S. Miller <davem@davemloft.net>