Fix install failure in google backend.

Instead of linking to libebook-google-utils.la, just add its source
files directly to the libebookbackendgoogle module.   So the code is
duplicated in the backend module and the noinst unit test library.

This was causing libtool to barf on bogus undefined reference errors
during install.  Still don't really understand what libtool's problem
was -- maybe it didn't like the noinst library?  Who knows.