nixos/nixseparatedebuginfod2: Relax too strict hardening

All debuginfo downloads were failing because downloading uses "nix
store --restore", which seems to need access to /proc. Blocking this
access via ProcSubset is even noted in systemd's documentation as
"not suitable for most non-trivial programs".

nixos/modules/services/development/nixseparatedebuginfod2.nix

@@ -87,7 +87,6 @@ in
         ProtectKernelLogs = true; # Prevent access to kernel logs
         ProtectClock = true; # Prevent setting the RTC
         ProtectProc = "noaccess";
-        ProcSubset = "pid";
 
         # Networking
         RestrictAddressFamilies = "AF_UNIX AF_INET AF_INET6";