drop property assignment to constants

[alexlamsl]

Only difference is with ember.prod.js under -mc passes=2 (or more)

master

http://builds.emberjs.com/tags/v2.11.0/ember.prod.js
- parse: 0.750s
- rename: 0.515s
- compress: 5.922s
- scope: 0.156s
- mangle: 0.313s
- properties: 0.000s
- output: 0.234s
- total: 7.890s

Original: 1852178 bytes
Uglified: 525313 bytes
GZipped:  128593 bytes
SHA1 sum: 5604c9f51b22ae0d38f652ed429e0e179c6261af

This PR

http://builds.emberjs.com/tags/v2.11.0/ember.prod.js
- parse: 0.734s
- rename: 0.594s
- compress: 5.828s
- scope: 0.141s
- mangle: 0.312s
- properties: 0.000s
- output: 0.313s
- total: 7.922s

Original: 1852178 bytes
Uglified: 525190 bytes
GZipped:  128563 bytes
SHA1 sum: 429e537397492cd76cdaf500f12f3f49d900ea5f

[alexlamsl]

Not to let test/ufuzz.js steals the spotlight, this PR was corrected by test/jetstream.js 😎