Remove internal class sun.net.www.MimeLauncher

MimeLauncher is a package-private class in the exported sun.net.www package in java.base. The class is no longer used in the package.

The sun.net.www package is exported to java.net.http and jdk.jartool. The only public access point to a MimeLauncher instance is MimeEntry::launch, which is not called anywhere in those two packages. MimeLauncher and MimeEntry::launch can thus be considered for removal.

Another related public class, sun.net.www. ApplicationLaunchException, is no longer used anywhere, and can also be considered for removal.