cdr.conf: Remove obsolete app_mysql reference.

The CDR sample config still mentions that app_mysql
is available in the addons directory, but this is
incorrect as it was removed as of 19. This removes
that to avoid confusion.

ASTERISK-30160 #close

Change-Id: Ie5293ccb4f2b365896981811b480544e67bb9cd7

configs/samples/cdr.conf.sample

@@ -102,8 +102,6 @@
 ; Here are all the possible back ends:
 ;
 ;   csv, custom, manager, odbc, pgsql, radius, sqlite, tds
-;    (also, mysql is available via the asterisk-addons, due to licensing
-;     requirements)
 ;   (please note, also, that other backends can be created, by creating
 ;    a new backend module in the source cdr/ directory!)
 ;