fix argument list of Sys.getenv

com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/SysFunctions.java

@@ -68,7 +68,7 @@ public class SysFunctions {
         }
     }
 
-    @RBuiltin(name = "Sys.getenv", kind = INTERNAL, parameterNames = {"x", "unset", "names"})
+    @RBuiltin(name = "Sys.getenv", kind = INTERNAL, parameterNames = {"x", "unset"})
     public abstract static class SysGetenv extends RBuiltinNode {
         private final ConditionProfile zeroLengthProfile = ConditionProfile.createBinaryProfile();