Remove unused "purgedirs" from documentation

purgedirs is only mentioned in the README.markdown file and the example
configuration file.  It is not used in the code.

Instead, the code purges the basedir for each source

Author: ssm

README.markdown

@@ -232,12 +232,6 @@ location is in /etc/r10k.yaml and can be specified on the command line.
         remote: '[email protected]:my-org/org-shared-modules'
         basedir: '/etc/puppet/environments'
 
-    # This directory will be purged of any directory that doesn't map to a
-    # git branch
-    :purgedirs:
-      - '/etc/puppet/environments'
-
-
 Multiple git repositories can be specified, which is handy if environments are broken up by application.
 Application 1 could have its own environment repository with app1_dev, app1_tst, and app1_prd branches while
 Application 2 could have its own environment repository with app2_dev, app2_tst, app2_prd branches.
@@ -265,13 +259,6 @@ without being able to accidentally impact other groups.
         remote: '[email protected]:my-org/app2-environments'
         basedir: '/etc/puppet/environments'
 
-    # This directory will be purged of any directory that doesn't map to a
-    # git branch
-    :purgedirs:
-      - '/etc/puppet/environments'
-
-
-
 More information
 ----------------
 

r10k.yaml.example

@@ -3,6 +3,3 @@
   :plops:
     remote: '[email protected]:my-org/org-shared-modules'
     basedir: '/etc/puppet/environments'
-
-:purgedirs:
-  - '/etc/puppet/environments'