feature.pl: Gen %feature_bundle from %UniqueBundles

feature.pl: Gen %feature_bundle from %UniqueBundles

%UniqueBundles was added for generating constants in feature.h, but
we can use it for feature.pm’s %feature_bundle as well, simplify-
ing the code.

This eliminates this piece of code in feature.pm, spelling it
out longhand:

# Each of these is the same as the previous bundle
for (12,13,14,16) {
    $feature_bundle{"5.$_"} = $feature_bundle{"5.".($_-1)}
}

While that code might be neat, it would make the generation code
unduly complex.  (It was designed for hand-editing anyway.)