EmbeddedBotWorker: Remove @-mention check.
EmbeddedBotWorker: Remove @-mention check.

We already check in get_service_bot_events() if a bot is mentioned,
and then only pass on the call to the bot handler if it is. The
commit removes the additional check in the embedded bot queue
processor simply because it is impossible to obtain test coverage
for it (there is no meaningful way to trigger the content of the
if-clause, because there will never be a message reaching the bot
without @-mentioning it.

To alleviate the danger of a potential regression, the check is not
removed completely, but rather replaced by an assert statement.

rishig/zulip,kou/zulip,brainwane/zulip,tommyip/zulip,rht/zulip,tommyip/zulip,timabbott/zulip,jackrzhang/zulip,shubhamdhama/zulip,brainwane/zulip,zulip/zulip,timabbott/zulip,punchagan/zulip,tommyip/zulip,rht/zulip,shubhamdhama/zulip,dhcrzf/zulip,kou/zulip,showell/zulip,hackerkid/zulip,hackerkid/zulip,hackerkid/zulip,shubhamdhama/zulip,rht/zulip,jackrzhang/zulip,dhcrzf/zulip,showell/zulip,showell/zulip,rht/zulip,jackrzhang/zulip,tommyip/zulip,rishig/zulip,dhcrzf/zulip,kou/zulip,synicalsyntax/zulip,eeshangarg/zulip,andersk/zulip,synicalsyntax/zulip,hackerkid/zulip,andersk/zulip,eeshangarg/zulip,dhcrzf/zulip,dhcrzf/zulip,brainwane/zulip,eeshangarg/zulip,kou/zulip,synicalsyntax/zulip,punchagan/zulip,tommyip/zulip,synicalsyntax/zulip,hackerkid/zulip,andersk/zulip,andersk/zulip,rishig/zulip,shubhamdhama/zulip,dhcrzf/zulip,zulip/zulip,rishig/zulip,eeshangarg/zulip,punchagan/zulip,synicalsyntax/zulip,brainwane/zulip,punchagan/zulip,showell/zulip,kou/zulip,rishig/zulip,shubhamdhama/zulip,jackrzhang/zulip,hackerkid/zulip,rht/zulip,kou/zulip,shubhamdhama/zulip,synicalsyntax/zulip,tommyip/zulip,jackrzhang/zulip,brainwane/zulip,kou/zulip,punchagan/zulip,jackrzhang/zulip,timabbott/zulip,dhcrzf/zulip,rht/zulip,zulip/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,timabbott/zulip,brainwane/zulip,eeshangarg/zulip,andersk/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,showell/zulip,timabbott/zulip,showell/zulip,zulip/zulip,timabbott/zulip,punchagan/zulip,andersk/zulip,rht/zulip,tommyip/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,rishig/zulip,zulip/zulip,jackrzhang/zulip,rishig/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip