Remove button:focus styles from _forms.scss

[DawidKK]

Proposed changes

Remove styling global button element in _forms.scss

button:focus {
  outline: none;
  background-color: $button-background-focus;
}

Now button styles are applied within .btn class

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.