Remove required class and fix helper message

[cicnavi]

Since 'authsource' is now an optional, this will remove 'required' CSS class in client create/edit form.
Also, helper message is fixes (appropriate translation key is now used).

[coveralls]

Pull Request Test Coverage Report for Build 361979158

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

---

Totals
Change from base Build 280672920:	0.0%
Covered Lines:	0
Relevant Lines:	1909

---

💛 - Coveralls

[sgomez]

Thanks!