[PRISM] Enable passing test_parenthesised_statement_argument

Author: kddnewton

test/.excludes-prism/TestSyntax.rb

@@ -20,7 +20,6 @@
 exclude(:test_methoddef_endless_command, "unknown")
 exclude(:test_numbered_parameter, "unknown")
 exclude(:test_optional_self_reference, "unknown")
-exclude(:test_parenthesised_statement_argument, "unknown")
 exclude(:test_safe_call_in_massign_lhs, "unknown")
 exclude(:test_syntax_error_at_newline, "unknown")
 exclude(:test_unassignable, "unknown")