trello: Remove unnecessary "is not supported" verbiage.
trello: Remove unnecessary "is not supported" verbiage.

UnexpectedWebhookEventType already encapsulates that it is not
supported, and having extra wording here disrupts how the exception
stringifies.

showell/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,showell/zulip,rht/zulip,zulip/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,andersk/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,zulip/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,showell/zulip,andersk/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,showell/zulip,eeshangarg/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,showell/zulip,kou/zulip,hackerkid/zulip,rht/zulip,kou/zulip,andersk/zulip,zulip/zulip,showell/zulip