BUG-4219: clean up features.xml

BUG-4219: clean up features.xml

In models' features.xml, odl-mdsal-binding-base includes yang-ext so
it's not strictly necessary in odl-mdsal-models. (This is potentially
controversial of course since it should perhaps be construed as a
declared part of the odl-mdsal-models API.)

In mdsal's features.xml:
* use odl-lmax-3 instead of odl-lmax;
* drop mdsal-dom-{api,spi} from odl-mdsal-dom-broker (they're part of
  odl-mdsal-dom-api);
* odl-mdsal-binding-api needs odl-yangtools-yang-parser, and
  mdsal-binding-util;
* odl-mdsal-singleton-dom needs odl-mdsal-common.

Change-Id: I4f18d697065f4e9df2b0e621fd32d4b18b8068fd
Signed-off-by: Stephen Kitt <skitt@redhat.com>