nasmdoc: remove obsolete Sourceforge references
nasmdoc: remove obsolete Sourceforge references

Remove obsolete Sourceforge references, replace with nasm.us.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,turingstudio/nasm,letolabs/nasm,projedi/nasm,letolabs/nasm,projedi/nasm,projedi/nasm,Distrotech/nasm,turingstudio/nasm,techkey/nasm,Distrotech/nasm,Distrotech/nasm,turingstudio/nasm,projedi/nasm,techkey/nasm,turingstudio/nasm,techkey/nasm,projedi/nasm,techkey/nasm,letolabs/nasm,Distrotech/nasm