yang-test POM simplification

yang-test POM simplification

Motivated by review https://git.opendaylight.org/gerrit/#/c/58714/, and
realizing that the odl-license version in this POM will cause issues
everytime we'll upgrade odplarent (which may be more frequent, soon).

This is effectively a counter proposal to c/58714, as on looking at this
it seems instead of bumping that version, we can remove most of what's
causing this (without loosing anything; CS still runs, not that we
care), becaues most of this is is inherited in Maven, the point of that
configuration is just to skip the VS validation which this project for
some reason exceptionally gen. into src/main instead of into target/.

The ${lifecycle.mapping.version} is replaced by fixed 1.0.0

Change-Id: Ic78c35a940dc7ee5fe25f3527529591e5c5214f7
Signed-off-by: Michael Vorburger <vorburger@redhat.com>