Remove support for Drupal 5 since we are adding support for Drupal 8.…

… 3 major versions of Drupal is quite enough. D5 sites are recommended to happily use drush4 ad infinitum.

README.txt

@@ -25,11 +25,9 @@ REQUIREMENTS
   GnuWin32 (http://gnuwin32.sourceforge.net/). More info
   about Drush on Windows available at http://drupal.org/node/594744.
 
-* Drush works with Drupal 5, Drupal 6 and Drupal 7.  However, occasionally
+* Drush works with Drupal 6, Drupal 7, and Drupal 8.  However, occasionally
   recent changes to the most recent version of Drupal can introduce issues
-  with Drush.  On Drupal 5, Drush requires update_status v5.x-2.5 or later
-  in order to use pm-updatecode.  If you have an earlier version of update_status,
-  upgrade it via "drush dl update_status" before using pm-updatecode.
+  with Drush.
 
 
 INSTALLATION

commands/core/archive.drush.inc

@@ -22,7 +22,6 @@ function archive_drush_command() {
       'drush archive-dump @sites' => 'Save archive containing all sites in a multi-site.',
       'drush archive-dump default --destination=/backups/mysite.tar' => 'Save archive to custom location.',
     ),
-    'core' => array('6+'),
     'bootstrap' => DRUSH_BOOTSTRAP_DRUPAL_SITE,
   );
   return $items;

commands/core/core.drush.inc

@@ -186,7 +186,7 @@ function core_drush_command() {
       'profile' => 'the install profile you wish to run. defaults to \'default\' in D6, \'standard\' in D7',
     ),
     'options' => array(
-      'db-url' => 'A Drupal 5/6 style database URL. Only required for initial install - not re-install.',
+      'db-url' => 'A Drupal 6 style database URL. Only required for initial install - not re-install.',
       'db-prefix' => 'An optional table prefix to use for initial install.',
       'account-name' => 'uid1 name. Defaults to admin',
       'account-pass' => 'uid1 pass. Defaults to a randomly generated password. If desired, set a fixed password in drushrc.php.',
@@ -203,7 +203,6 @@ function core_drush_command() {
       'drush site-install --db-url=sqlite:/full/path/to/database.sqlite' => 'Install using SQLite (D7 only).',
       'drush site-install --account-name=joe --account-pass=mom' => 'Re-install with specified uid1 credentials.',
     ),
-    'core' => array('6+'),
     'bootstrap' => DRUSH_BOOTSTRAP_DRUPAL_ROOT,
     'aliases' => array('si'),
     'deprecated-aliases' => array('installsite', 'is'),