Make the new script portable: remove all non-portable constructs, and rename
and re-#! the script accordingly.

* tools/dev/remove-trailing-whitespace.zsh: Edit as above, and rename to..
* tools/dev/remove-trailing-whitespace.sh: .. this.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1467190 13f79535-47bb-0310-9956-ffa450edef68