Proposal for TS API in 9.2.1: Remove TSSslSecretXxx functions

[Walt Karas]

https://github.com/apache/trafficserver/pull/9587 indicates they do not
work.  There are no definite plans to fix them.  So, seems they are
unlikely to be fixed before the release of 9.2.1.  Fixing or removing them
in 10.0 is a related but separate issue.