nixd: general cleanups #1433

Job	Run time
nix-build-develop-clang (none, release, true)	5m 23s
nix-build-develop-clang (none, release, false)	4m 30s
nix-build-develop-clang (none, debug, true)	3m 49s
nix-build-develop-clang (none, debug, false)	5m 42s
nix-build-develop-gcc (none, release, true)	4m 49s
nix-build-develop-gcc (none, release, false)	6m 8s
nix-build-develop-gcc (none, debug, true)	4m 30s
nix-build-develop-gcc (none, debug, false)	5m 33s
nix-build-develop-gcc (undefined, release, true)	12m 48s
nix-build-develop-gcc (undefined, release, false)	12m 28s
nix-build-develop-gcc (undefined, debug, true)	5m 30s
nix-build-develop-gcc (undefined, debug, false)	6m 41s
	1h 17m 51s

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