Make sure Rib scripts that make use of first class worker support don't produce fully qualified function names in error messages

[afsalthaj]

• All error messages in golem rib should just specify the final method name. This is the only way out to making rib more generic especially when used directly from wasmtime
• All tests that checks the error messages should be updated with only method name and not fully qualified name

[vigoo]

Closing as we won't further develop Rib.