fix(memory-utilization): don't keep bounded reference of connection manager (#8760)

lib/dialects/abstract/connection-manager.js

@@ -43,9 +43,9 @@ class ConnectionManager {
       Promise
     });
 
-    // Save a reference to the bound version so we can remove it with removeListener
-    this._onProcessExit = this._onProcessExit.bind(this);
-    process.on('exit', this._onProcessExit);
+    process.on('beforeExit', () => {
+      this._onProcessExit.call(this);
+    });
 
     this.initPools();
   }
@@ -85,9 +85,6 @@ class ConnectionManager {
    * @return {Promise}
    */
   close() {
-    // Remove the listener, so all references to this instance can be garbage collected.
-    process.removeListener('exit', this._onProcessExit);
-
     // Mark close of pool
     this.getConnection = function getConnection() {
       return Promise.reject(new Error('ConnectionManager.getConnection was called after the connection manager was closed!'));