Only use Healthz from index.ts

Not really sure how useful it is anyways?

src/Mjolnir.ts

@@ -360,7 +360,6 @@ export class Mjolnir {
             }
 
             this.currentState = STATE_RUNNING;
-            Healthz.isHealthy = true;
             await this.logMessage(LogLevel.INFO, "Mjolnir@startup", "Startup complete. Now monitoring rooms.");
         } catch (err) {
             try {

src/health/healthz.ts

@@ -16,7 +16,7 @@ limitations under the License.
 
 import * as http from "http";
 import { LogService } from "matrix-bot-sdk";
-// allowed to use the global configuration since there should only be one of these anyways.
+// allowed to use the global configuration since this is only intended to be used by `src/index.ts`.
 import config from '../config';
 
 export class Healthz {

src/index.ts

@@ -63,6 +63,7 @@ if (config.health.healthz.enabled) {
     }
     try {
         await bot.start();
+        Healthz.isHealthy = true;
     } catch (err) {
         console.error(`Mjolnir failed to start: ${err}`);
         throw err;