examples: rename "-example" suffix from examples files

The suffix is redundant since the containing directory itself is
called "examples". Simplify.

doc/examples/Makefile

@@ -3,7 +3,7 @@ FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
 CFLAGS+=$(shell pkg-config  --cflags $(FFMPEG_LIBS))
 LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))
 
-EXAMPLES=encoding-example muxing-example
+EXAMPLES=encoding muxing
 
 OBJS=$(addsuffix .o,$(EXAMPLES))