Remove the last utility functions for handling the multi-cert bundles
and remove the multi-variable from the ckch structure.
With this patch, the bundles are completely removed.
Since the removal of the multi-certificates bundle support, this
variable is not useful anymore, we can remove all tests for this
variable and suppose that every ckch contains a single certificate.
Add some functions to deinit the whole crtlist and ckch architecture.
It will free all crtlist, crtlist_entry, ckch_store, ckch_inst and their
associated SNI, ssl_conf and SSL_CTX.
The SSL_CTX in the default_ctx and initial_ctx still needs to be free'd
separately.
