phone: Disable documentation

Derivations like the documentation for rustc were taking up huge amounts
of space that *probably* aren't needed on the PinePhone, so disabling
documentation should significantly improve copy times and reduce the
total amount of space necessary for updates.

hosts/phone/configuration.nix

@@ -292,7 +292,10 @@ in
     };
   };
 
-  documentation.man.generateCaches = false;
+  documentation = {
+    enable = false;
+    man.generateCaches = false;
+  };
 
   hardware.graphics.enable32Bit = mkForce false;