[TECHNICAL-SUPPORT] LPS-48933 Remove [$USER_AGENT$] placeholder from the UI, as it isn't replaced since LPS-22979 for security reasons

Hi Eduardo,

LPS-22979 removed the [$USER_AGENT$] placeholder replacement for security reasons, however, the UI still indicates that in the notification emails it will be replaced. 
That's why I removed it from the UI as well.

Could you please review my changes?

Thanks,
Tamás