staging: greybus: kernel_ver.h: remove lots of stuff

Now that we do not care about the kernel version we are building
against, we can strip out lots of backward compatibilty that was added
to kernel_ver.h in order to write semi-portable driver code.

To start with, remove the functions and #defines that are now in the
kernel tree, no need to have duplicate copies of them all.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>