Revert workarounds for JDK 9+ due to missing Scala Native methods

[ekrich]

Look for nnnL for Long and toLong in the following methods. Most are in the second argument, first in one case.

public static long multiplyExact​(long x, int y)
public static long floorDiv​(long x, int y)
public static int floorMod​(long x, int y)

The classes affected are LocalDate, Instant, Duration, Year, and YearMonth.
The test classes are LocalDateTest, YearTest and YearMonthTest.

[ekrich]

These are implemented now as of 1-27-2023.