[DOCS] Default names for CRL and CA files in the backend

Commit a445cb92ef5b3a31313ebce30e18cc1d6e0bdecb removed the default names for
serverside CRL and CA files, but the defaults were left in the "SSL Server File
Usage” table with a small note.  I completely missed the note, even after
having been fiddling about with the code in question.  Removing the filenames
from the table, and altering the note per the attached patch, makes the docs
clearer IHMO.

cheers ./daniel