Remove use of non-existent MaterialAppearance.VERTEX_FORMAT

There were a few places in the code we were using `MaterialAppearance.VERTEX_FORMAT`,
which is `undefined`.  I've replaced this with `MaterialAppearance.MaterialSupport.TEXTURED.vertexFormat`,
which is the actual value used in cases where no `vertexFormat` is provided.  There
is no actual change in behavior.
Merge pull request #2249 from AnalyticalGraphicsInc/vertexFormat-cleanup

Remove use of non-existent MaterialAppearance.VERTEX_FORMAT