Deleting old 2.3 v file

git-svn-id: https://plugins.svn.wordpress.org/a-very-simple-captcha/trunk@813151 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added new 2.4 version readme file

git-svn-id: https://plugins.svn.wordpress.org/a-very-simple-captcha/trunk@813152 b8457f37-d9ea-0310-8a92-e5e31aec5664