biology/seaview: unbreak the port's build against FLTK 1.3.10

Currently used formula tries to fold FLTK version triple into
an integer (100 * FL_MAJOR_VERSION + 10 * FL_MINOR_VERSION +
FL_PATCH_VERSION < 140) but this fails once the patch version
had reached 10. Drop it from the calculation entirely because
FLTK hasn't been breaking API and ABI for last several 1.3.x
releases, and accounting for it now makes little to no sense.

Reported by: pkg-fallout