Remove tests for the '/' variable operator.

This is a Bash-specific feature, which means that it is out of scope
for now.

* tests/variable-patterns.org (slash, slash-string,
slash-string-slash): Delete tests.

tests/variable-patterns.org

@@ -72,32 +72,3 @@
 #+begin_example
   --prefix=/usr/
 #+end_example
-
-* slash
-:script:
-#+begin_src sh
-  var='xxfooxx'
-  echo "${var/foo}"
-#+end_src
-:stdout:
-#+begin_example
-  xxxx
-#+end_example
-
-* slash-string
-:script:
-#+begin_src sh
-  var='xxfooxx'
-  echo "${var/foo/bar}"
-#+end_src
-:stdout:
-#+begin_example
-  xxbarxx
-#+end_example
-
-* slash-string-slash
-:script:
-#+begin_src sh
-  var='xxfooxx'
-  echo "${var/foo/bar/}"
-#+end_src