Remove the event queue code

Remove the event queue code

PR #18345 added some code for an event queue. It also added a test for it.
Unfortunately this event queue code has never been used for anything.
Additionally the test was never integrated into a test recipe, so it never
actually gets invoked via "make test". This makes the code entirely dead,
unnecessarily bloats the size of libssl and causes a decrease in our
testing code coverage value.

We remove the dead code.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25100)