Remove "-break-insert -r" tests

PR mi/14270 points out that mi-break.exp has some tests for an
unimplemented "-r" switch for "-break-insert".  This switch was never
implemented, and is not documented -- though it is mentioned in a
comment in the documentation.  This patch removes the test and the doc
comment.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=14270