Manager: remove --factory-startup from default Blender arguments

Remove `--factory-startup` from the default Blender arguments. This makes
it simpler to configure each Worker to use its own GPU, without having to
inject Python code into the arguments.

Users can always add this when they need, but I think it's friendlier to
have Blender behave the same when they manually run it and when used by
Flamenco Worker.

internal/manager/config/defaults.go

@@ -9,7 +9,7 @@ import (
 
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-const DefaultBlenderArguments = "--factory-startup -b -y"
+const DefaultBlenderArguments = "-b -y"
 
 // The default configuration, use DefaultConfig() to obtain a copy.
 var defaultConfig = Conf{