lavc: deprecate CODEC_CAP_NEG_LINESIZES

It was never used in any codec since it was added 3 years ago.

libavcodec/avcodec.h

@@ -762,10 +762,12 @@ typedef struct RcOverride{
  * Codec should fill in channel configuration and samplerate instead of container
  */
 #define CODEC_CAP_CHANNEL_CONF     0x0400
+#if FF_API_NEG_LINESIZES
 /**
- * Codec is able to deal with negative linesizes
+ * @deprecated no codecs use this capability
  */
 #define CODEC_CAP_NEG_LINESIZES    0x0800
+#endif
 /**
  * Codec supports frame-level multithreading.
  */

libavcodec/version.h

@@ -115,5 +115,8 @@
 #ifndef FF_API_FAST_MALLOC
 #define FF_API_FAST_MALLOC       (LIBAVCODEC_VERSION_MAJOR < 56)
 #endif
+#ifndef FF_API_NEG_LINESIZES
+#define FF_API_NEG_LINESIZES     (LIBAVCODEC_VERSION_MAJOR < 56)
+#endif
 
 #endif /* AVCODEC_VERSION_H */