Man writer: improvements to code and code blocks.

The aim here (see #9020) is to produce more standard and more
portable man pages.  To that end:

- We revert the fanciness introduced in #7506, which employs a
  custom font name V and a macro that makes this act like boldface
  in a terminal and monospace in other formats.  Unfortunately,
  this code uses a mechanism that is not portable (and does not
  work in mandoc).

- Instead of using V for inline code, we simply use CR.
  Note that `\f[CR]` is emitted instead of plain `\f[C]`,
  because there is no C font in man.  (This produces warnings
  in recent versions of groff.)

- For code blocks, we now use the `.EX` and `.EE` macros,
  together with `.IP` for spacing and indentation.  This gives
  more standard code that can be better interpreted e.g. by mandoc.

data/templates/default.man

@@ -5,20 +5,6 @@ $if(pandoc-version)$
 .\" Automatically generated by Pandoc $pandoc-version$
 .\"
 $endif$
-.\" Define V font for inline verbatim, using C font in formats
-.\" that render this, and otherwise B font.
-.ie "\f[CB]x\f[]"x" \{\
-. ftr V B
-. ftr VI BI
-. ftr VB B
-. ftr VBI BI
-.\}
-.el \{\
-. ftr V CR
-. ftr VI CI
-. ftr VB CB
-. ftr VBI CBI
-.\}
 $if(adjusting)$
 .ad $adjusting$
 $endif$