nixos/qemu-vm: default memorySize 384 -> 1024

the default hasn't been changed since 2009
this can improve our test performances

nixos/tests: remove explicit memorySize <1024

1024MiB is now the default

nixos/tests/mysql/mysql.nix

@@ -64,10 +64,6 @@ in
       {
         imports = [ users ];
 
-        # prevent oom:
-        # Kernel panic - not syncing: Out of memory: compulsory panic_on_oom is enabled
-        virtualisation.memorySize = 1024;
-
         services.mysql.enable = true;
         services.mysql.initialDatabases = [
           { name = "testdb3"; schema = ./testdb.sql; }