[ci] Remove jestSequencer

This was previously used for circleci parallelization but is no longer
needed.

ghstack-source-id: d8c1005
Pull Request resolved: #30500

Author: poteto

scripts/jest/config.base.js

@@ -24,8 +24,6 @@ module.exports = {
   },
   snapshotSerializers: [require.resolve('jest-snapshot-serializer-raw')],
 
-  testSequencer: require.resolve('./jestSequencer'),
-
   testEnvironment: 'jsdom',
 
   testRunner: 'jest-circus/runner',