Avoid lifting try block in argument of static method into separate methods

[lrytz]

Suggested in https://github.com/scala/scala/pull/7312#issuecomment-430893978

class C {
  def b = 0
  def t = java.util.Collections.singletonList(try b catch { case _: ClassCastException => b })
}

The argument is lifted into a method by uncurry, but that's not necessary as there's no value on the stack.

[SethTisue]

(Not sure what the right label is to apply here — "backend" typically refers to GenBCode, but uncurry is somewhere in the "middle end".)

[sjrd]

Fixed in Scala 3 by https://github.com/lampepfl/dotty/pull/18619