Remove clone() and "implements Cloneable" from android.icu.number.Precision and ScientificNotation

The API was first made public in R. This API change will be made into
the same platform version.

Bug: 151133612
Test: m droid
Merged-In: Ic251b4b0d7b2896b14bc55c3b09093c06600b16b
Change-Id: Ic251b4b0d7b2896b14bc55c3b09093c06600b16b
(cherry picked from commit c6dcd534)