refactor(3p/nix): Remove remaining prefork-compat type

Removes the verbosity enum, which is no longer actively used anywhere
other than a daemon protocol implementation bit that doesn't actually
work.

Since the verbosity was marked deprecated, this removes one of the
last remaining warnings.

Change-Id: Iaee9d1d6c14b30daac83bb44bcacff32a0e07fb0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1289
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

third_party/nix/src/libutil/CMakeLists.txt

@@ -18,7 +18,6 @@ set(HEADER_FILES
     lru-cache.hh
     monitor-fd.hh
     pool.hh
-    prefork-compat.hh
     ref.hh
     serialise.hh
     sync.hh

third_party/nix/src/libutil/prefork-compat.hh

@@ -1,21 +0,0 @@
-// This file exists to preserve compatibility with the pre-fork
-// version of Nix (2.3.4).
-//
-// During the refactoring, various structures are getting ripped out
-// and replaced with the dummies below while code is being cleaned up.
-
-#ifndef NIX_SRC_LIBUTIL_PREFORK_COMPAT_H_
-#define NIX_SRC_LIBUTIL_PREFORK_COMPAT_H_
-
-namespace nix::compat {
-
-// This is used in remote-store.cc for various things that expect the
-// old logging protocol when talking over the wire. It will be removed
-// hen the worker protocol is redone.
-enum [[deprecated("old logging compat only")]] Verbosity{
-    kError = 0, kWarn, kInfo, kTalkative, kChatty, kDebug, kVomit,
-};
-
-}  // namespace nix::compat
-
-#endif  // NIX_SRC_LIBUTIL_PREFORK_COMPAT_H_