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>