Remove enyo.execUnsafeFunction, instead do runtime check once and short ...

...but for common non-IE cases. Idea suggested by Roy Sutton.

Remove msapp checks from enyo.machine.script/sheet because we don't support MSApp's with load-time script loading, only minified versions. Better to error out with a security failure here than to load things in wrong order.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)