Replace -bootclasspath and -classpath metalava options with --classpath

Metalava has not differentiated between bootclasspath and classpath for
years so this change replaces the use of the two deprecated single
hyphen options with `--classpath`.

Bug: 295136054
Test: m checkapi
Change-Id: I3ab20b76a60cab66a27784b7d87a069813d19835