gssd: Be consistent about Makefile conditionals

[ivy]

Summary

gssd itself is only built when both MK_GSSAPI and MK_KERBEROS_SUPPORT
are enabled, but the init script and OptionalObsoleteFiles entries
only checked MK_GSSAPI. Check both variables everywhere.

[des]

tools/build/mk/OptionalObsoleteFiles.inc

6899

while we're here, can you please double-check if this section is correct?

[rmacklem]

Thanks for doing this. I was going to start looking at this
to-day, but I'm glad to see you've done it.