Remove mention of monkey patching tests from README

We used to have to monkey patch by hand, but now we are able to use the
mock package instead, which is generally less cumbersome.

See commit 1756c89, for the final
removal of this directory.

Signed-off-by: mulhern <[email protected]>

Author: mulkieran

tests/README.txt

@@ -2,7 +2,6 @@ This directory contains tests of the CLI functionality.
 
 There are three directories containing three types of tests:
 * unit - strict unit tests which require no setup of the environment
-* monkey_patching - tests that use monkey_patching to mock some behavior
 * integration - straightforward tests of functionality
 
 The project Makefile has make targets for running these different categories