staging: wilc1000: remove define TCP_ENHANCEMENTS and it's related code

TCP_ENHANCEMENTS is always in use. Remove define TCP_ENHANCEMENTS, ifdef line,
ifndef line and codes inside ifndef.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>