Remove $IGNORECASE

`$=` has been obsolete and has no effect since 1.9.

Author: nobu

lib/English.rb

@@ -39,7 +39,6 @@
 # $PROCESS_ID:: $$
 # $CHILD_STATUS:: $?
 # $LAST_MATCH_INFO:: $~
-# $IGNORECASE:: $=
 # $ARGV:: $*
 # $MATCH:: $&
 # $PREMATCH:: $`
@@ -151,9 +150,6 @@ module English end if false
 # scope.
 alias $LAST_MATCH_INFO $~
 
-# This variable is no longer effective. Deprecated.
-alias $IGNORECASE $=
-
 # An array of strings containing the command-line
 # options from the invocation of the program. Options
 # used by the Ruby interpreter will have been