Tweak -Wconf:help for correctness

[som-snytt]

Fixes #19885

Used no LLM except Lukas the Language Manager on Scala 2. All remaining faults are my own, however.

[som-snytt]

Per current behavior.

scala-cli repl --server=false -S 3.8.2 -Wall -Wconf:any:e -Wconf:cat=deprecation:s
Welcome to Scala 3.8.2 (25, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> 42 formatted "%d"
val res0: String = "42"

scala> class C { private val x = 42 }
-- [E198] Unused Symbol Error: -------------------------------------------------
1 |class C { private val x = 42 }
  |                      ^
  |                      unused private member
1 error found

scala>

just checking...

scala-cli repl --server=false -S 3.8.2 -Wall -deprecation
Welcome to Scala 3.8.2 (25, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> 42 `formatted` "%d?"
1 warning found
-- Deprecation Warning: --------------------------------------------------------
1 |42 `formatted` "%d?"
  |^^^^^^^^^^^^^^
  |method formatted in class StringFormat is deprecated since 2.12.16: Use `formatString.format(value)` instead of `value.formatted(formatString)`,
  |or use the `f""` string interpolator. In Java 15 and later, `formatted` resolves to the new method in String which has reversed parameters.
val res0: String = "42?"

scala> "hi".formatted("%s!")
val res1: String = "hi"

scala>