Revert iter28b DIAG: trim=40 universal-trim breaks IDR frame 1

iter28b tested LIBVA_HEVC_TRIM_TRAILING=40 on HEVC. Result: hash
differed at byte 899745 (inside frame 1, NOT just frame 2 boundary at
byte 1382401). Trimming 40 bytes off the IDR slice (96890→96850)
corrupted frame 1. The 40-byte inflation is not uniform per slice;
requires dynamic detection (e.g., scan for rbsp_stop_one_bit) or
per-slice-type logic.

src/picture.c

@@ -61,32 +61,13 @@ static VAStatus codec_store_buffer(struct request_data *driver_data,
 				   struct object_buffer *buffer_object)
 {
 	switch (buffer_object->type) {
-	case VASliceDataBufferType: {
+	case VASliceDataBufferType:
 		/*
 		 * Since there is no guarantee that the allocation
 		 * order is the same as the submission order (via
 		 * RenderPicture), we can't use a V4L2 buffer directly
 		 * and have to copy from a regular buffer.
 		 */
-		size_t slice_bytes = buffer_object->size * buffer_object->count;
-
-		/*
-		 * iter28b DIAG (env-gated): trim trailing N bytes from
-		 * VAAPI's slice_data buffer for HEVC. Tests the hypothesis
-		 * that ffmpeg-vaapi inflates slice_data_size vs
-		 * ffmpeg-v4l2request. Set LIBVA_HEVC_TRIM_TRAILING=N to
-		 * trim. For BBB frame 2 with libva 5549 vs kdirect 5509:
-		 * try N=40.
-		 */
-		if (profile == VAProfileHEVCMain) {
-			const char *trim_env = getenv("LIBVA_HEVC_TRIM_TRAILING");
-			if (trim_env) {
-				unsigned long t = strtoul(trim_env, NULL, 0);
-				if (t < slice_bytes)
-					slice_bytes -= t;
-			}
-		}
-
 		if (context->h264_start_code) {
 			static const char start_code[3] = { 0x00, 0x00, 0x01 };
 
@@ -98,11 +79,11 @@ static VAStatus codec_store_buffer(struct request_data *driver_data,
 		memcpy(surface_object->source_data +
 			       surface_object->slices_size,
 		       buffer_object->data,
-		       slice_bytes);
+		       buffer_object->size * buffer_object->count);
-		surface_object->slices_size += slice_bytes;
+		surface_object->slices_size +=
+			buffer_object->size * buffer_object->count;
 		surface_object->slices_count++;
 		break;
-	}
 
 	case VAPictureParameterBufferType:
 		switch (profile) {