EIP712 Message text is shown twice

**Describe the bug**
When signing a message as per the EIP712 standard, the word "Message" shows up twice, which looks wierd.

**Steps to reproduce (REQUIRED)**
Sign any EIP712 standard message.

1. Example on [codesandbox](https://codesandbox.io/s/gracious-raman-id9cg?file=/src/index.js)
2. Connect your wallet and click on the sign button

**Expected behavior**
Only show the "Message" text once

Use the linked CodeSandbox's src/index.js and its EIP712 signing flow to reproduce the duplicated label. Then trace the corresponding signing UI entry point in the extension and compare the rendered headings with the expected single “Message” label. Done means signing an EIP712 message displays “Message” only once.

Written by the indexing model from the issue text.