Revert "selftest: net: Test IPv4 PMTU exceptions with DSCP and ECN"

This reverts commit a7246d39 which is
commit ec730c3e upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I075725477959ad747c01910ec658efafe0dd98ba
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>