Hoist ParseErrorReporter into style and remove the dependency on msg.

The pipeline id stuff is currently unused. If someone needs it, they can add
an additional trait bound on their css error reporter to get the pipeline id.

components/style/parser.rs

@@ -4,7 +4,7 @@
 
 
 use cssparser::{Parser, SourcePosition};
-use msg::ParseErrorReporter;
+use error_reporting::ParseErrorReporter;
 use selectors::parser::ParserContext as SelectorParserContext;
 use stylesheets::Origin;
 use url::Url;