[v2] os: drop SUN-DES-1 authentication

Here's an draft for dropping the outdated SUN-DES-1 authentication entirely. See discussion in !1441 (merged).

Short summary:

• relies on RPC DES authentication method, which is being dropped by more and more platforms
• FTBS on NetBSD 10 (which already dropped DES)
• superseeded by better auth methods
• dating back to time before local client creds could be retrieved from sockets (eg. getpeereid() et al).
• even on Solaris, build-time disabled for about a decade now
• doesn't seem to be practically used anymore

Changes v2:

• dropped some more remains in the build files
• dropped draft status