[gssproxy] [gssapi/gssproxy] 803d92: Clarify mech_for_saslname implementation note

[Simo Sorce]

  Branch: refs/heads/main
  Home:   https://github.com/gssapi/gssproxy
  Commit: 803d92a76b565a2b95469c5bb1224075a450df74
      https://github.com/gssapi/gssproxy/commit/803d92a76b565a2b95469c5bb122407...
  Author: Simo Sorce <simo(a)redhat.com&gt;
  Date:   2020-10-28 (Wed, 28 Oct 2020)

  Changed paths:
    M src/mechglue/gpp_indicate_mechs.c

  Log Message:
  -----------
  Clarify mech_for_saslname implementation note

There is nothing to actually fix in this function unless we change how
interposing works. Add a note and remove the FIXME.

Signed-off-by: Simo Sorce <simo(a)redhat.com&gt;