Makefile: remove unused variable ALLHTMLPAGES

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit f3619680)

Makefile

@@ -23,7 +23,6 @@ BASENAMES   = ffmpeg ffplay ffprobe ffserver
 ALLPROGS    = $(BASENAMES:%=%$(EXESUF))
 ALLPROGS_G  = $(BASENAMES:%=%_g$(EXESUF))
 ALLMANPAGES = $(BASENAMES:%=%.1)
-ALLHTMLPAGES= $(BASENAMES:%=%.html)
 
 FFLIBS-$(CONFIG_AVDEVICE) += avdevice
 FFLIBS-$(CONFIG_AVFILTER) += avfilter