Deprecate USE_RELINE and USE_REIDLINE

Based on this commit: 93f87ec

It appears that the maintainer @aycabta wanted to deprecate any `USE_*LINE` configs in favor of
`USE_MULTILINE`. So we should deprecate `USE_RELINE` as well.

Author: st0012

lib/irb/context.rb

@@ -49,10 +49,13 @@ def initialize(irb, workspace = nil, input_method = nil)
       if IRB.conf.has_key?(:USE_MULTILINE)
         @use_multiline = IRB.conf[:USE_MULTILINE]
       elsif IRB.conf.has_key?(:USE_RELINE) # backward compatibility
+        warn <<~MSG.strip
+          USE_RELINE is deprecated, please use USE_MULTILINE instead.
+        MSG
         @use_multiline = IRB.conf[:USE_RELINE]
       elsif IRB.conf.has_key?(:USE_REIDLINE)
         warn <<~MSG.strip
-          USE_REIDLINE is deprecated, please use USE_RELINE instead.
+          USE_REIDLINE is deprecated, please use USE_MULTILINE instead.
         MSG
         @use_multiline = IRB.conf[:USE_REIDLINE]
       else