MFC r212390: expr(1): Add sh(1) versions of examples, remove an incorrect

MFC r212390: expr(1): Add sh(1) versions of examples, remove an incorrect
example.

The three examples are better done using sh(1) itself these days.

The example
  expr -- "$a" : ".*"
is incorrect in the general case, as "$a" may be an operator.

git-svn-id: svn://svn.freebsd.org/base/stable/8@213079 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f