Remove unnecessary rake tasks to switch shells

The test/shells script has a better technique of doing this anyhow.  The cp
wasn't working on unix distros.

Makefile

@@ -8,24 +8,3 @@ ronn/bin/ronn:
 man/man1/ts.1: README.md ronn/bin/ronn
 	mkdir -p man/man1
 	ruby -Ironn/lib ronn/bin/ronn -r --pipe --organization="$(VERSION)" --date="$(DATE)" $< > $@
-
-/bin/sh.bak:
-	sudo cp /bin/sh /bin/sh.bak
-
-sh: /bin/sh.bak
-	sudo cp /bin/sh.bak /bin/sh
-
-bash: /bin/sh.bak
-	sudo cp $$(command -v bash) /bin/sh
-
-dash: /bin/sh.bak
-	sudo cp $$(command -v dash) /bin/sh
-
-zsh: /bin/sh.bak
-	sudo cp $$(command -v zsh) /bin/sh
-
-csh: /bin/sh.bak
-	sudo cp $$(command -v csh) /bin/sh
-
-ksh: /bin/sh.bak
-	sudo cp $$(command -v ksh) /bin/sh