avcodec/proresdec2: Rename to proresdec

Once upon a time, there used to be a LGPL and a GPL ProRes decoder
in FFmpeg; the current decoder evolved from the second of these.
But given that it is now the only ProRes decoder we have, it's file
should simply be named proresdec.c (which also brings it in line with
its header).

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

libavcodec/Makefile

@@ -608,7 +608,7 @@ OBJS-$(CONFIG_PNG_DECODER)             += png.o pngdec.o pngdsp.o
 OBJS-$(CONFIG_PNG_ENCODER)             += png.o pngenc.o
 OBJS-$(CONFIG_PPM_DECODER)             += pnmdec.o pnm.o
 OBJS-$(CONFIG_PPM_ENCODER)             += pnmenc.o
-OBJS-$(CONFIG_PRORES_DECODER)          += proresdec2.o proresdsp.o proresdata.o
+OBJS-$(CONFIG_PRORES_DECODER)          += proresdec.o proresdsp.o proresdata.o
 OBJS-$(CONFIG_PRORES_ENCODER)          += proresenc_anatoliy.o proresdata.o
 OBJS-$(CONFIG_PRORES_AW_ENCODER)       += proresenc_anatoliy.o proresdata.o
 OBJS-$(CONFIG_PRORES_KS_ENCODER)       += proresenc_kostya.o proresdata.o