[Platform] Remove incorrect isProxy check

Errant isProxy check caused node views to fail
to report their parent views in certain situations,
resulting in nasa/mct#261, wherein the Move
option is incorrectly suppressed by dragging
and dropping.

Also included is unit test to exercise method
and detect regression.
Merge pull request #262 from VWoeltjen/mct261

[Platform] Remove incorrect isProxy check