Lower precision for a number of queries.

These queries are currently run by default, but don't have their results displayed.

Looking through results on LGTM.com, they are either false positives (e.g., `BitwiseSignCheck` which flags many perfectly harmless operations and `CompareIdenticalValues` which mostly flags NaN checks) or harmless results that developers are unlikely to care about (e.g., `EmptyArrayInit` or `MisspelledIdentifier`).

With this PR, the only queries that are still run but not displayed are security queries, where different considerations may apply.

javascript/ql/src/AngularJS/DeadAngularJSEventListener.ql

@@ -3,7 +3,7 @@
  * @description An AngularJS event listener that listens for a non-existent event has no effect.
  * @kind problem
  * @problem.severity warning
- * @precision medium
+ * @precision low
  * @id js/angular/dead-event-listener
  * @tags correctness
  *       frameworks/angularjs

javascript/ql/src/AngularJS/UnusedAngularDependency.ql

@@ -3,7 +3,7 @@
  * @description Unused dependencies are confusing, and should be removed.
  * @kind problem
  * @problem.severity recommendation
- * @precision high
+ * @precision low
  * @id js/angular/unused-dependency
  * @tags maintainability
  *       frameworks/angularjs