Remove outdated pins

Author: LukasAud

.fixtures.yml

@@ -1,15 +1,9 @@
 fixtures:
   repositories:
-    sshkeys_core:
-      repo: 'https://github.com/puppetlabs/puppetlabs-sshkeys_core'
-      puppet_version: '>= 6.0.0'
-    stdlib:
-      repo: 'https://github.com/puppetlabs/puppetlabs-stdlib.git'
-      ref: '5.0.0'
+    sshkeys_core: 'https://github.com/puppetlabs/puppetlabs-sshkeys_core'
+    stdlib: 'https://github.com/puppetlabs/puppetlabs-stdlib.git'
     facts: 'https://github.com/puppetlabs/puppetlabs-facts.git'
-    puppet_agent:
-      repo: 'https://github.com/puppetlabs/puppetlabs-puppet_agent.git'
-      ref: v4.21.0
+    puppet_agent: 'https://github.com/puppetlabs/puppetlabs-puppet_agent.git'
     provision: 'https://github.com/puppetlabs/provision.git'
   symlinks:
     accounts: "#{source_dir}"