build: install the Info and Html manuals even when 'makeinfo' is missing

If the system on which nano is configured does not have the 'makeinfo'
program installed, the prebuilt and packaged nano.info and nano.html
should nevertheless be installed.

Also, the TEXINFOS primary has built-in rules for generating HTML files
from the texinfo sources, so an explicit rule is not needed.

This indirectly addresses https://savannah.gnu.org/bugs/?49969.

configure.ac

@@ -733,10 +733,6 @@ else
 fi
 AM_CONDITIONAL(GROFF_HTML, test x$groff_html_support = xyes)
 
-# Check for the availability of makeinfo.
-AC_CHECK_PROG(haveit, makeinfo, yes, no)
-AM_CONDITIONAL(HAVE_MAKEINFO, test x$haveit = xyes)
-
 # Check whether this is a git repository.
 AC_MSG_CHECKING([whether building from git])
 if test -d .git ; then

doc/Makefile.am

@@ -25,11 +25,9 @@ endif
 
 info_TEXINFOS = nano.texi
 
-if HAVE_MAKEINFO
 BUILT_SOURCES += nano.html
-endif
+dist_html_DATA += nano.html
 
-nano.html: nano.texi
-	makeinfo --no-split --html < $< > $@
+AM_MAKEINFOHTMLFLAGS = --no-split
 
 EXTRA_DIST = $(BUILT_SOURCES) $(info_TEXINFOS)