Omit "V" at the start of DEFVAR_BOOL vars

Omit "V" at the start of DEFVAR_BOOL vars

Problem noted by Stefan Monnier in:
https://lists.gnu.org/r/emacs-devel/2020-08/msg00846.html
* src/font.c (xft_ignore_color_fonts):
* src/syntax.c (comment_end_can_be_escaped):
* src/xdisp.c (word_wrap_by_category, display_fill_column_indicator):
Rename these DEFVAR_BOOL variables to avoid the initial "V"
that wrongly suggests that they are Lisp_Object variables.
All uses changed.