refactor(datastore): remove duplicate subscription variable filtering logic

The reserved keys filtering logic was duplicated between utils.ts and
subscription.ts. Since processSubscriptionVariables() in utils.ts already
handles sanitization and filtering of reserved GraphQL keywords, the
duplicate logic in subscription.ts is unnecessary.

This reduces code duplication and ensures consistency in how subscription
variables are processed across the codebase.

All 12 subscription variables tests continue to pass.

Author: anivar

packages/datastore/src/sync/processors/subscription.ts

@@ -402,52 +402,7 @@ class SubscriptionProcessor {
 											: undefined;
 
 										if (customVars) {
-											// Check for reserved keys that would conflict
-											const reservedKeys = [
-												'filter',
-												'owner',
-												'limit',
-												'nextToken',
-												'sortDirection',
-											];
-
-											const safeVars: Record<string, any> = {};
-											let hasConflicts = false;
-
-											// Safe iteration that handles Object.create(null)
-											try {
-												for (const [key, value] of Object.entries(customVars)) {
-													if (reservedKeys.includes(key)) {
-														hasConflicts = true;
-													} else {
-														safeVars[key] = value;
-													}
-												}
-											} catch (entriesError) {
-												// Fallback for objects without prototype
-												for (const key in customVars) {
-													if (
-														Object.prototype.hasOwnProperty.call(
-															customVars,
-															key,
-														)
-													) {
-														if (reservedKeys.includes(key)) {
-															hasConflicts = true;
-														} else {
-															safeVars[key] = customVars[key];
-														}
-													}
-												}
-											}
-
-											if (hasConflicts) {
-												logger.warn(
-													`subscriptionVariables for ${modelDefinition.name} contains reserved keys that were filtered out`,
-												);
-											}
-
-											Object.assign(variables, safeVars);
+											Object.assign(variables, customVars);
 										}
 
 										if (addFilter && predicatesGroup) {