classpath: Use generic check for host program

Remove the specific check that was done in dependencies.sh to use the
generic one that were introduced by the previous patch.

Also, introduce, BR2_NEEDS_HOST_JAVAC and BR2_NEEDS_HOST_JAR as it is
needed by classpath.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Reviewed-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>