EventEmitter: Remove redundant 'if' statement in off()

This was added when we fixed a bug in disconnect() where it
threw due to accessing an undefined property if there were no
events bound yet.

However, off(), unlike disconnect(), never had this bug. The 'if'
statement is redundant as the 'delete' operator checks this
already. We don't use its return value either (which is true/false
for whether it deleted something).

Increases code coverage by removing implicit 'else' branches that
were never ran.

Change-Id: I40cba9292ad851757fc2a605f0ddc66df0ea173f
test: Add test for passing EventEmitter#connect a function

Increasing test coverage.

I'm not sure why this feature exists since passing a function
here basically just does a regular .on() binding. The given
function has no relation to the host object passed to connect().

But we currently support it, so might as well test it.

Change-Id: I805dd75611cca407f43fce86d0521df4307e26d0