Remove single-argument function call special-case in formatter

Not sure what this special case was trying to achieve, but it's not right. There's no need to handle function call with a single argument differently than the others.

examples/acceptance_tests/035/lib/aiken/dict.ak

@@ -19,8 +19,8 @@ pub fn insert(
   value v: value,
 ) -> Dict<key, value> {
   Dict {
-  inner: do_insert_with(self.inner, k, v, fn(_, left, _right) { Some(left) })}
-  
+    inner: do_insert_with(self.inner, k, v, fn(_, left, _right) { Some(left) }),
+  }
 }
 
 pub fn union_with(