Remove deprecated implementation of payment method label under gateway settings #13

[mehul0810]

Description

This PR resolves #13

How Has This Been Tested?

I've tested this PR by changing the payment method label as per Give core 2.0.0 functionality.

Types of changes

Bug fix (a non-breaking change which fixes an issue)

Checklist:

• [x] My code is tested.
• [x] My code follows the WordPress code style.
• [x] My code follows has proper inline documentation.