Remove unnecessary fboundp checks in fd-stream.lisp.

Don't check for FINALIZE and CANCEL-FINALIZATION to be fbound before
calling them.
Deinit various variables during core saving.

Things like *default-pathname-defaults* and *runtime-pathname* do not
need to be saved into the image. This also fixes a problem when
*machine-version* wasn't updated even when the image was transferred
to another machine.