fix(@opentelemetry/exporter-collector): remove fulfilled promises correctly

Author: aabmass

packages/opentelemetry-exporter-collector/src/platform/browser/CollectorExporterBrowserBase.ts

@@ -68,19 +68,14 @@ export abstract class CollectorExporterBrowserBase<
     const serviceRequest = this.convert(items);
     const body = JSON.stringify(serviceRequest);
 
-    const promise = new Promise(resolve => {
+    const promise = new Promise<void>((resolve) => {
       const _onSuccess = (): void => {
         onSuccess();
-        _onFinish();
+        resolve();
       };
       const _onError = (error: collectorTypes.CollectorExporterError): void => {
         onError(error);
-        _onFinish();
-      };
-      const _onFinish = () => {
         resolve();
-        const index = this._sendingPromises.indexOf(promise);
-        this._sendingPromises.splice(index, 1);
       };
 
       if (this._useXHR) {
@@ -97,5 +92,10 @@ export abstract class CollectorExporterBrowserBase<
       }
     });
     this._sendingPromises.push(promise);
+    const _onFinish = () => {
+      const index = this._sendingPromises.indexOf(promise);
+      this._sendingPromises.splice(index, 1);
+    };
+    promise.then(_onFinish);
   }
 }