Remove dead code in sun.misc.FormattedFloatingDecimal class

sun.misc.FormattedFloatingDecimal was created to support the implementation of java.util.Formatter and the following methods are used by the Formatter class.
  getChars()
  getExponent()
  getExponentRounded()

Several methods (e.g. readJavaFormatString()) that are copied from sun.misc.FloatingDecimal are not used anywhere. They can be removed.