don't inherit allowed deprecation from parent modules

Inheriting allow-deprecation from parent modules doesn't make too much
sense, so instead make them default to disallow unless otherwise
specified. This allows build system to avoid redundant
`-fno-allow-deprecated` args.

This makes the generated CLIs smaller, and makes zig1.wasm update not
needed.

Also represented `is_root` differently (moved to field of graph).

src/Package/Module.zig

@@ -238,7 +238,6 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
 
     const allow_deprecated = b: {
         if (options.inherited.allow_deprecated) |x| break :b x;
-        if (options.parent) |p| break :b p.allow_deprecated;
         break :b false;
     };