Remove mention on focus for same person multiple time.

[Sushma-tiwari]

Remove mention on focus for same person multiple time.

Describe the bug or issue here…

Steps to Reproduce
In base camp trix press @ then user list show like snap https://prnt.sc/1922ix3
And select same user multiple time.
Now focus on 2nd user it will always focus 1st user https://prnt.sc/19230tn
Details
After mention multiple time same user focus on it confuse https://prnt.sc/19230tn

Expect Result: When I select 2nd user at that time focus should be applied to the 2nd user, not 1st user.

Trix version: 1.3.1
Browser name and version: Chrome and 91.0.4472.124
Operating system: Windows