These errors are printed because your classpath contains a file that specifies the availability of this parser. Please make sure that the file(s) called /META-INF/services/org.openrdf.rio.RDFParserFactory only specify the parsers that are available.
Thanks for that knowledge!
I went and looked at my imported files and found the file in the common-1.2.jar file that is published by https://github.com/joshsh/sesametools
I am using that package for its rdf-json parser and writer, and didn't realise that it was including other parser regitry entries that it doesn't provide. I have filed a bug with that project to remove the unnecessary files.
It is a very neat way of publishing this information by the way!