[PATCH v2 4/5] contrib/subtree/Makefile: Doc-gen rules cleanup

git:Documentation/Makefile establishes asciidoc/xmlto calls as being handled through their appropriate variables, Hence, change to bring into congruency with. Similarly, MANPAGE_XSL exists in git:Documentation/Makefile, while MANPAGE_NORMAL_XSL does not outside contrib/subtree. Hence, replace

[PATCH v2 4/5] contrib/subtree/Makefile: Doc-gen rules cleanup

git:Documentation/Makefile establishes asciidoc/xmlto calls as being handled through their appropriate variables, Hence, change to bring into congruency with. Similarly, MANPAGE_XSL exists in git:Documentation/Makefile, while MANPAGE_NORMAL_XSL does not outside contrib/subtree. Hence, replace