US 1-405 general Harmonize font for tuple representing direct base class relationship

[wg21bot]

The tuple representing direct base class relationships is sometimes in code font (e.g., 6.7 bullet 16.4.2; 11.7.1 paragraph 2) and sometimes not (e.g., 21.4.6 bullet 2.5).

Proposed change:

Decide on one style and apply it throughout.

[jensmaurer]

Do not use code font; this is abstract territory.