stddoclet: Clean up package page when dir has package.html but no source files

It is now possible to create documentation on a package that contains
a package.html file but has no source files. Take this source tree:

./pkg/package.html
./pkg/subpkg/C1.java

% javadoc pkg pkg.subpkg

The package-summary.html page looks like:

   ----------------------------------------------
   Package pkg

   This is the package description. <--CLUTTER 1

   See: <--CLUTTER 2
          Description <--CLUTTER 3

   Package pkg Description <--CLUTTER 4

   This is the package description. This is the
   second sentence.
   ----------------------------------------------

Because there is no class summary on this page,
the lines marked CLUTTER should be omitted.

CLUTTER 1 is a copy of the first sentence.
CLUTTER 2 and CLUTTER 3 is a link to CLUTTER 4

In other words, inserting the "clutter" should
be conditional on whether there is one or more classes
in this package.