[cleanup] Move BREEs to JavaSE-1.8

org.eclipse.amalgam.discovery.modeling declared a BREE of J2SE-1.5,
but did not compile with an actual JRE 1.5 as it (indirectly) depends
on Java 8 types.

Move all the BREEs to JavaSE-1.8 to be more consistent, and because
this is already the minimum version needed by many dependencies.

Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
Change-Id: I0c0247a79ac59813ddb90fd10799d2f4ee8f3740