Remove syck YAML extension
The syck extension should be removed for the following reasons:
Syck only supports YAML 1.0
Syck is not YAML 1.0 compliant.
Syck is not easy to maintain, and many of the bugs existing in it have not been fixed.
Psych uses libyaml for YAML parsing of 1.0 and 1.1 documents.
The libyaml parser is maintained by a third party and shared by many projects so we benefit from bug fixes from a broad user base.
It is too hard to type "Syck" vs "Psych" I often type "Sych" or "Psyck" (joke).