Tron: Unify introductory layout actions (Cancel vs X)

**Introductory layout inconsistencies in Tron flows**
- "Cancel" label in the menu vs "X" icon on the main screen creates UX inconsistency.
- Reference: [Full flow](https://data.trezor.io/dev/firmware/ui_report/22168463751/passed/T3W1_en-device_tests-tron-test_sign_tx.py::test_sign_tx%5BApprove_TRC-20%5D.html)

![Intro layout inconsistency](image3)