nixos: default nix.maxJobs to auto

Instead of making the configuration less portable by hard coding the number of
jobs equal to the cores we can also let nix set the same number at runtime.

nixos/modules/installer/tools/nixos-generate-config.pl

@@ -91,9 +91,6 @@ sub hasCPUFeature {
 }
 
 
-# Detect the number of CPU cores.
-my $cpus = scalar (grep {/^processor\s*:/} (split '\n', $cpuinfo));
-
 
 # Determine CPU governor to use
 if (-e "/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors") {
@@ -562,7 +559,6 @@ my $hwConfig = <<EOF;
   boot.kernelModules = [$kernelModules ];
   boot.extraModulePackages = [$modulePackages ];
 $fsAndSwap
-  nix.maxJobs = lib.mkDefault $cpus;
 ${\join "", (map { "  $_\n" } (uniq @attrs))}}
 EOF