Removed obsolete test cases from tests/libebook

Removed obsolete test cases from tests/libebook

Removed the following cases:

	deleted:    test-bulk-methods.c
	deleted:    test-changes.c
	deleted:    test-ebook-async.c
	deleted:    test-ebook-stress-factory--fifo.c
	deleted:    test-ebook-stress-factory--serial.c
	deleted:    test-ebook-stress-factory--single-book.c
	deleted:    test-ebook.c
	deleted:    test-nonexistent-id.c
	deleted:    test-search.c
	deleted:    test-self.c
	deleted:    test-stress-bookviews.c

Many of these tests are covered by other cases, some of them are
completely unsupported now (like test-changes.c).

The ebook-test-utils.[ch] has been cleaned up to remove book
creation / opening routines (which is now all covered by the
test fixture).