Mk/**octave.mk: Convert to USES=octave

As part of the improvements of USES infrastructure Mk/bsd.octave.mk has
been converted to Mk/Uses/octave.mk. This also declutters some old
stuffs in the octave-* ports and makes it simpler to add more
octave-forge ports easily.

While I am here make all the ports portclippy/portfmt compliant. And use
USES macros whenever possible.

Reviewed by: portmgr
Approved by: tcberner
Differential Revision: https://reviews.freebsd.org/D37887