bitbake: [parser] Kill obtain/localpath from the parser

bitbake: [parser] Kill obtain/localpath from the parser

With obtain it was possible to use an existing fetcher to
download a bb or config file. In practive no one has used it
and it was likely broken in regard to depends_cache... Remove
it for now, simplfiy the code.

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>