Revert "Keg: allow overwriting same-formula conflicts"

Library/Homebrew/keg.rb

@@ -647,15 +647,6 @@ class Keg
     dst.delete if options[:overwrite] && (dst.exist? || dst.symlink?)
     dst.make_relative_symlink(src)
   rescue Errno::EEXIST => e
-    # Retry if we're linking a different version of the same
-    # formula. The `AlreadyLinkedError` above won't catch
-    # this if a formula is missing an optlink. In that case,
-    # delete the symlink and retry.
-    if dst.symlink? && dst.exist? && Keg.for(dst).name == name
-      dst.unlink
-      retry
-    end
-
     raise ConflictError.new(self, src.relative_path_from(path), dst, e) if dst.exist?
 
     if dst.symlink?