Remove duplicated exception in Ci config

This is a temporary refactoring stub, that is planned to be removed
after removing legacy config processor.

lib/ci/gitlab_ci_yaml_processor.rb

@@ -18,7 +18,7 @@ module Ci
       initial_parsing
       validate!
-    rescue Gitlab::Ci::Config::LoaderError => e
+    rescue Gitlab::Ci::Config::Loader::FormatError => e
       raise ValidationError, e.message
     end

lib/gitlab/ci/config.rb

@@ -5,11 +5,6 @@ module Gitlab
       def initialize(config)
         loader = Loader.new(config)
-
-        unless loader.valid?
-          raise LoaderError, 'Invalid configuration format!'
-        end
-
         @config = loader.load
       end

spec/lib/gitlab/ci/config_spec.rb

@@ -37,7 +37,8 @@ describe Gitlab::Ci::Config do
       describe '.new' do
         it 'raises error' do
           expect { config }.to raise_error(
-            Gitlab::Ci::Config::LoaderError, /Invalid configuration format/
+            Gitlab::Ci::Config::Loader::FormatError,
+            /Invalid configuration format/
           )
         end
       end