tests/Makefile: Remove FILTERDEMDECMUX

It is unused and given that one needs an encoder to produce
packets from AVFrames (as output by filters) this is likely
to remain so, because FILTERDEMDECENCMUX is better for these
scenarios.
The only case where one can use filters without encoders is
with the lavfi input device: It outputs AVPackets which could
be copied without another conversion to AVFrames. Yet the variable
to check for this is CONFIG_LAVFI_INDEV, but FILTERDEMDECMUX
is designed to work with demuxers (i.e. CONFIG_*_DEMUXER).
So there is no usecase for FILTERDEMDECMUX.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

tests/Makefile

@@ -111,7 +111,6 @@ FRAMECRC = $(call ALLYES, $(1)_DEMUXER $(2:%=%_DECODER) $(3)                  \
 DEMMUX  = $(call ALLYES, $(1)_DEMUXER $(2)_MUXER $(3) FILE_PROTOCOL)
 
 FILTERDEMDEC       = $(call ALLYES, $(1:%=%_FILTER) $(2)_DEMUXER $(3)_DECODER $(4) FILE_PROTOCOL)
-FILTERDEMDECMUX    = $(call ALLYES, $(1:%=%_FILTER) $(2)_DEMUXER $(3)_DECODER $(4)_MUXER   $(5) FILE_PROTOCOL)
 FILTERDEMDECENCMUX = $(call ALLYES, $(1:%=%_FILTER) $(2)_DEMUXER $(3)_DECODER $(4)_ENCODER $(5)_MUXER $(6) FILE_PROTOCOL)
 
 PARSERDEMDEC       = $(call ALLYES, $(1)_PARSER $(2)_DEMUXER $(3)_DECODER $(4) FILE_PROTOCOL)