AVRO-3403: minor fix

share/idl_grammar/org/apache/avro/idl/Idl.g4

@@ -34,10 +34,7 @@ grammar Idl;
 
 // \u001a is the ascii 'sub'(stitute) character, used as end-of-file marker in older systems. It was also used as "end of character stream".
 // Thus, accept it at end of the input and ignore anything that comes after it. (See: https://en.wikipedia.org/wiki/Substitute_character)
-idlFile: (
-    protocol=protocolDeclaration |
-    namespace=namespaceDeclaration? mainSchema=mainSchemaDeclaration? (imports+=importStatement|namedSchemas+=namedSchemaDeclaration)*
-) ('\u001a' .*?)? EOF;
+idlFile: protocol=protocolDeclaration ('\u001a' .*?)? EOF;
 
 protocolDeclaration: (doc=DocComment)? schemaProperties+=schemaProperty* Protocol name=identifier body=protocolDeclarationBody;