Remove TODO file for 2.5 branch

TODO

-Leftover bits from ITS#8294 -- Drop custom SHA2 code, use default crypto library SHA2 functions instead
-  May need to document minimum crypto library version requirements
-  Can also include sha2.c in slapd-sha2.c and make everything static
-
-New syslog engine
-
-[12:45] <hyc> I meant regcomp and regexec
-[12:45] <hyc> mainly - compile a pattern, then fill in substitution parameters later
-[12:46] <hyc> yes but the idea is still based on numbered substitution parameters
-[12:47] <hyc> it's a pretty obvious approach, and with regex, time-tested.
-[12:48] <hyc> I may try to sneak it into OpenLDAP 2.5