Simplify some make rules

A rule of type "a/%: a/%.in" will also match "a/b/%: a/b/%.in", so no
need for the explicit examples/hooks rule. As for the man rules, they
are identical and thus can be collapsed.

We still have the problem that globally, not all our %.in to %
transformations are identical; this is suboptimal and should be
cleaned sometime…

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>