Remove unneeded $: property in component

This was left over from when ChangeMemberRoleModal handled both project
and org memberships, and needed to adjust its schema based on the
now-removed roleType prop.

frontend/src/routes/(authenticated)/project/[project_code]/ChangeMemberRoleModal.svelte

@@ -9,7 +9,7 @@
 
   export let projectId: string;
 
-  $: schema = z.object({
+  const schema = z.object({
     role: z.enum([ProjectRole.Editor, ProjectRole.Manager])
   });
   type Schema = typeof schema;