Remove obsolete build_manpages target and markdown type

They're based on obsolete mkit.ini structure and is not used in any known
project.  That said, at least build_manpages will be added in future,
most probably in form of plugin, once plugin structure is figured out.
(Stay tuned, but don't hold your breath!)

src/include/build.sh

     local ftype=$1      # file/builder type
     case $ftype in
         MKIT_COMMON)    _expand_tokens "tokens" ;;
-        markdown)       _expand_includes | _expand_tokens "tokens" ;;
         rpmstuff)       _expand_tokens "tokens" "rpmstuff:tokens" ;;
         debstuff)       _expand_tokens "tokens" "debstuff:tokens" ;;
         *)              die "unknown file type: $ftype" ;;
     esac
 }
 
-_expand_includes() {
-    #
-    # Expand include directives
-    #
-    # Expand e.g. `<!-- include4: foo.sh -->` to include code of foo.sh
-    #
-    perl -we '
-        use strict;
-        my $text;
-        while (<>) {
-            chomp;
-            if (m/<!-- include4: (\S+) -->/) {
-                open my $fh, $1 or warn "cannot find: $1";
-                my $text = do { local($/); <$fh> };
-                close $fh;
-                $text =~ s/^(.)/    $1/gm;
-                chomp $text;
-                print "$text\n";
-            } else {
-                print "$_\n";
-            }
-        }
-    '
-}
-
 _expand_tokens() {
     #
     # Read stdin, expanding tokens from sections $@
     #
     local dstpath=$1    # destination path
     case $dstpath in
-        *.md) echo markdown    ;;
         *)    echo MKIT_COMMON ;;
     esac
 }
        done
 }
 
-build_manpages() {
-    #
-    # Build manpages using ronn
-    #
-    local manfile   # each manual file listed in '[files:man]'
-    local mdfile    # each source markdown file
-    if command -v ronn >/dev/null; then
-        ini lskeys "files:man" \
-          | while read -r manfile; do
-                mdfile="$manfile.md"
-                ronn -r "$mdfile"
-                rec_built "$manfile"
-            done
-    else
-        echo "ronn is not installed"
-        return 1
-    fi
-}
-
 clean() {
     #
     # Clean up tree after building

src/include/mkit.sh

     # List valid routes
     #
     echo build
-    echo build_manpages
     echo clean
     echo debstuff
     echo dist

src/mkit.mk

 build:
 	@"$(MKIT_DIR)"/make build
 
-manpages: build
-	@"$(MKIT_DIR)"/make build_manpages
-
 clean:
 	@"$(MKIT_DIR)"/make clean