(maint) Remove symlink check in Travis CI

Previously Travis CI was emitting false negative failures for the symlink
check.  This was due to a gem having symlinks in it, and Travis bundles gems
into ./vendor which the rake task should ignore. Until this is is fixed in
https://tickets.puppetlabs.com/browse/PDK-1199 this commit removes the symlink
check from Travis as Appveyor already does this test.

.sync.yml

@@ -35,5 +35,14 @@ appveyor.yml:
 .gitlab-ci.yml:
   delete: true
 
+# Due to https://tickets.puppetlabs.com/browse/PDK-1199 we need to stop the symlink checks in Travis CI
+# The symlink checks are still done in Appveyor so there's no loss in coverage
+.travis.yml:
+  includes:
+    - env: CHECK="syntax lint metadata_lint check:git_ignore check:dot_underscore check:test_file rubocop"
+    - env: CHECK=parallel_spec
+    - env: PUPPET_GEM_VERSION="~> 4.0" CHECK=parallel_spec
+      rvm: 2.1.9
+
 spec/default_facts.yml:
   unmanaged: true

.travis.yml

@@ -20,8 +20,9 @@ env:
 matrix:
   fast_finish: true
   include:
+    # PDK Update doesn't replace this line, but instead adds a new one.
     -
-      env: CHECK="syntax lint metadata_lint check:symlinks check:git_ignore check:dot_underscore check:test_file rubocop"
+      env: CHECK="syntax lint metadata_lint check:git_ignore check:dot_underscore check:test_file rubocop"
     -
       env: CHECK=parallel_spec
     -