Revert "BACKPORT: kernel: add kcov code coverage"

This reverts commit f945a3c1.

Revert this unused feature. It is starting to complicate 3.18 LTS merges
and it is not a base or recommended option. It is not being used any
more.

Bug: 116647072
Change-Id: I46253472a1b4429b1a87c27deea529f4c3eb4a36
Signed-off-by: Alistair Strachan <astrachan@google.com>