package.bbclass: Skip testing "packages" a second time.

package.bbclass: Skip testing "packages" a second time.

Since the "packages" variable is already tested a few lines above in
the same routine:

    if len(packages) < 1:
        bb.debug(1, "No packages to build, skipping do_package")
        return

there is no point testing it again, and the error message doesn't even
refer to "packages", anyway.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Saul Wold <sgw@linux.intel.com>