revert(select): avoid checking option element selected properties in render

This reverts commit dc149de9364c66b988f169f67cad39577ba43434.

This commit fixes a bug caused by Firefox updating `select.value` on hover. However, it
causes other bugs with select including the issue described in #7715. This issue causes
selects with a blank disabled option to skip to the second option. We filed a bug
with Firefox for the problematic behavior this commit addresses
https://bugzilla.mozilla.org/show_bug.cgi?id=1039047, and alternate Angular fixes are being
investigated. The test introduced in this commit does test a valid case and is therefore not
reverted.
test(select): add test cases for selects with blank disabled options
An earlier commit dc149de9364c66b988f169f67cad39577ba43434 caused an error where the first option of
a select would be skipped over if it had a blank disabled value. These tests demonstrate that with
that commit in place, blank disabled options are skipped in a select. When the commit is reverted,
the correct behavior is seen that the blank disabled option is still selected in both selects
marked with required and those that have optional choices.

Relates to #7715
test(select): add test of updating the model because of ng-change

A regression #7855 was introduced by
https://github.com/angular/angular.js/commit/dc149de9364c66b988f169f67cad39577ba43434
This test ensures that reverting that commit fixes this regression.
In the regression, changes to a bound model in ng-change were not propagated back to the view.