Keeping the relevant 'ssl_scache' in 'data->state' leads to problems
when the owner of the cache is cleaned up and this reference is left
dangling.
Remove the ref entirely and always find the ssl_scache at the current
share or multi.
Folded in #16260 (test 3208) to verify this fixes the bug with a
dangling reference when an easy handle is used with easy_perform first
and in a multi_perform after.
Ref: #16236Closes#16261
