Revert "TerminalDxe: select the UART's default receive FIFO depth"

Revert "TerminalDxe: select the UART's default receive FIFO depth"

This reverts commit 31ae446b1a039a55d0336f2201d77d1032533413.
Changing the receive FIFO depth in Terminal driver Start() is not
recommended.
A new PCD PcdUartDefaultReceiveFifoDepth was added and
MdeModulePkg/SerialDxe driver uses the PCD as the default receive
FIFO depth.

Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>