Eliminate JDK build dependency of native2ascii and update Japanese nroff man pages to UTF-8 encoding

Proposal has been made to remove "native2ascii" tool from JDK9.

It was identified that JDK9 uses "native2ascii" itself to convert Japanese nroff man pages to various encodings (Linux: UTF-8, Solaris: UTF-8, PCK/SJIS) from eucJP source.

  define install-ja-manpage
        $(MKDIR) -p $(@D)
        $(CAT) $< \
            | $(NATIVE2ASCII) -encoding eucJP \
            | $(SED) 's/@@VERSION@@/$(THIS_JDK_VERSION)/g' \
            | $(NATIVE2ASCII) -reverse -encoding $1 \
            > $@
  endef

Since the supported Solaris and Linux OS releases now support UTF-8 locales by default, we should just deliver UTF-8 encoded nroff man pages and eliminate the conversion process.