devtool: Drop oe-local-files and simplify

devtool: Drop oe-local-files and simplify

The only real reason for oe-local-files was to support S = WORKDIR. With changes to
drop support for that, it makes sense to simplify devtool and to try and make both
the code and the processes/workflows simpler.

This patch drops support for S = WORKDIR, removes oe-local-files and then updates
the test cases to match this new situation.

At the code level, we assume we can always now track code changes using git and
that things committed into git are handled as patches (as before) but delta against
HEAD is saved as specific file level changes to the recipe.

One test is disabled as it is no longer approproate. It is being keped until we can
make WORKDIR != UNPACKDIR at which point it should be revisited.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>