Revert "net: Add driver helper functions to determine checksum offloadability"

This reverts commit 6ae23ad3

.

The code has been in kernel since 4.4 but there are no in tree
code that uses. Unused code is broken code, remove it.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>