doc: remove explicit formatting of terms in definition lists

Sphinx-doc already formats the terms appropriately for a given
backend (bold in html and man). `makeinfo` complains noisily about
formatting inside a @item if we add our own explicit formatting.

This change may change the formatting in the info output. On the other
hand, the existing use of quotes for bold is not that great anyway.

In some places blank lines were removed to preserve the logical
structure of a definition list.