build: clean up BUILT_SOURCES

build: clean up BUILT_SOURCES

BUILT_SOURCES doesn't do what the name suggests.  What it actually means
is "these files should be built first when doing a 'make' without
explicit target" (or "make all").

It's pretty much almost always wrong to use BUILT_SOURCES, the only
correct use is when a file is needed by an unspecified / large set of
files.

Also remove version.h and route_types.h from dist tarball while we're at
it.  configure will create them anyway.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>