Fix incorrect Android-changed markers in String.java.

This change notes that the String(char[], boolean) constructor is
removed and the String(int, int, char[]) constructor is added. The
markers in http://r.android.com/501921 missed the change in signature.

Test: make checkbuild
Change-Id: Iae3c4c9c153fc0c6fc36c4e637c5a3705ea8b996