Remove the current version in "Information for Downloading" from the Readme.md file.

This was missed in #2722 and was also missed for the 2.19 release
obviously.  So by deleting it from the file it won't be missed again!

Author: drgrice1

README.md

@@ -26,8 +26,6 @@ New users interested in getting started with their own WeBWorK server, or instru
 
 ## Information for Downloading
 
-* The current version is WeBWorK-2.18 and its companion PG-2.18
-
 * Installation manuals can be found at https://webwork.maa.org/wiki/Category:Installation_Manuals
 
 ## Information For Developers