docs: simplify the docs build a tiny bit
docs: simplify the docs build a tiny bit

HTML_TARGETS includes MAN_HTML_TARGETS, so when we depend on HTML_TARGETS
we don't need to also depend on MAN_HTML_TARGETS.

Signed-off-by: Sebastian Kuzminsky <62d754cc350e84d3b1c32ae79f976f5348e74a40@highlab.com>

ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror