perf(ngOptions): avoid calls to element.value

In some cases IE11/Edge calls to `element.value` are very slow when the
`element.value` has not been set. Normally, these calls are usualy 0-3 ms
but in these cases it can take 200-300 ms. This can easily add 3 or more
seconds to the load time on a view that has 10 or more select tags using
`ngOptions`.

The line this pull request is changing not only suffers from the performance
issue described above but it also appears to be broken. The code is checking
that `option.value` does not equal `element.value` but then sets `element.value`
to `option.selectValue`.

I don't believe `option.value` is actually defined anywhere and likely it
was always intended to be `option.selectValue`. This means that check would
always be true and since this code has been this way for quite a while and
is causing a performance issue I've just removed the check. This way a call
to `element.value` is never made prior to it's value being set.

Closes #15344

src/ng/directive/ngOptions.js

@@ -591,7 +591,7 @@ var ngOptionsDirective = ['$compile', '$document', '$parse', function($compile,
           element.label = option.label;
           element.textContent = option.label;
         }
-        if (option.value !== element.value) element.value = option.selectValue;
+        element.value = option.selectValue;
       }
 
       function updateOptions() {