iter36: remove env-gated DIAG probes (iter29/30/33/35)

Cleans up the campaign's exploratory env-gated dumps now that all
bugs are fixed:
- iter29 LIBVA_HEVC_DUMP_SLICE_TAIL (h265.c) — refuted 40-byte inflation theory
- iter30 LIBVA_TS_SCALE (picture.c) — refuted timestamp magnitude theory
- iter33 LIBVA_VP8_DUMP_FRAME (vp8.c) — led to α-30 fix
- iter35 LIBVA_MPEG2_DUMP_FRAME (mpeg2.c) — confirmed MPEG-2 ctrls correct

Total: -131 lines / +7 lines (α-7 comment refresh).

Preexisting framework env knobs retained:
- LIBVA_V4L2_DUMP_OUTPUT (picture.c α-16)
- LIBVA_V4L2_DUMP_CAPTURE (surface.c)
- LIBVA_V4L2_ZERO_CAPTURE (picture.c)
- LIBVA_V4L2_REQUEST_VIDEO_PATH / MEDIA_PATH / NO_AUTODETECT (request.c)

The 3 load-bearing fixes remain unchanged:
α-25 (rkvdec image_fmt pre-seed, src/context.c)
α-29 (slice_params.short_term_ref_pic_set_size, src/h265.c)
α-30 (VP8 OUTPUT header prepend, src/picture.c)

src/vp8.c

@@ -59,8 +59,6 @@
 
 #include <assert.h>
 #include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 
 #include <sys/ioctl.h>
@@ -246,71 +244,6 @@ int vp8_set_controls(struct request_data *driver_data,
 	if (picture->pic_fields.bits.sign_bias_alternate)
 		frame.flags |= V4L2_VP8_FRAME_FLAG_SIGN_BIAS_ALT;
 
-	/* iter33 DIAG: dump v4l2_ctrl_vp8_frame contents.
-	 * LIBVA_VP8_DUMP_FRAME=1 enables. */
-	if (getenv("LIBVA_VP8_DUMP_FRAME")) {
-		uint8_t *p = (uint8_t *)&frame;
-		uint32_t k;
-		fprintf(stderr,
-			"vp8: width=%u height=%u version=%u flags=0x%llx num_dct=%u\n",
-			frame.width, frame.height, frame.version,
-			(unsigned long long)frame.flags, frame.num_dct_parts);
-		fprintf(stderr,
-			"vp8: first_part_size=%u first_part_header_bits=%u prob_skip_false=%u prob_intra=%u prob_last=%u prob_gf=%u\n",
-			frame.first_part_size, frame.first_part_header_bits,
-			frame.prob_skip_false, frame.prob_intra,
-			frame.prob_last, frame.prob_gf);
-		fprintf(stderr,
-			"vp8: lf level=%u sharpness=%u flags=0x%x ref_frm_delta=[%d %d %d %d] mb_mode_delta=[%d %d %d %d]\n",
-			frame.lf.level, frame.lf.sharpness_level, frame.lf.flags,
-			frame.lf.ref_frm_delta[0], frame.lf.ref_frm_delta[1],
-			frame.lf.ref_frm_delta[2], frame.lf.ref_frm_delta[3],
-			frame.lf.mb_mode_delta[0], frame.lf.mb_mode_delta[1],
-			frame.lf.mb_mode_delta[2], frame.lf.mb_mode_delta[3]);
-		fprintf(stderr,
-			"vp8: quant y_ac=%u y_dc_d=%d y2_dc_d=%d y2_ac_d=%d uv_dc_d=%d uv_ac_d=%d\n",
-			frame.quant.y_ac_qi, frame.quant.y_dc_delta,
-			frame.quant.y2_dc_delta, frame.quant.y2_ac_delta,
-			frame.quant.uv_dc_delta, frame.quant.uv_ac_delta);
-		fprintf(stderr,
-			"vp8: seg flags=0x%x quant_update=[%d %d %d %d] lf_update=[%d %d %d %d]\n",
-			frame.segment.flags,
-			frame.segment.quant_update[0], frame.segment.quant_update[1],
-			frame.segment.quant_update[2], frame.segment.quant_update[3],
-			frame.segment.lf_update[0], frame.segment.lf_update[1],
-			frame.segment.lf_update[2], frame.segment.lf_update[3]);
-		fprintf(stderr,
-			"vp8: coder range=%u value=%u bit_count=%u\n",
-			frame.coder_state.range, frame.coder_state.value,
-			frame.coder_state.bit_count);
-		fprintf(stderr, "vp8: dct_part_sizes=[");
-		for (k = 0; k < 8; k++)
-			fprintf(stderr, "%u%s", frame.dct_part_sizes[k],
-				k < 7 ? " " : "]\n");
-		fprintf(stderr,
-			"vp8: refs last=%llu golden=%llu alt=%llu\n",
-			(unsigned long long)frame.last_frame_ts,
-			(unsigned long long)frame.golden_frame_ts,
-			(unsigned long long)frame.alt_frame_ts);
-		fprintf(stderr, "vp8: entropy y_mode_probs=[%u %u %u %u] uv_mode_probs=[%u %u %u]\n",
-			frame.entropy.y_mode_probs[0], frame.entropy.y_mode_probs[1],
-			frame.entropy.y_mode_probs[2], frame.entropy.y_mode_probs[3],
-			frame.entropy.uv_mode_probs[0], frame.entropy.uv_mode_probs[1],
-			frame.entropy.uv_mode_probs[2]);
-		fprintf(stderr, "vp8: coeff_probs[0][0][0][0..11]=");
-		for (k = 0; k < 11; k++)
-			fprintf(stderr, "%u ", frame.entropy.coeff_probs[0][0][0][k]);
-		fprintf(stderr, "\n");
-		fprintf(stderr, "vp8: VAAPI-src probability_set=%d dct_coeff_probs[0][0][0][0..11]=",
-			probability_set);
-		for (k = 0; k < 11; k++)
-			fprintf(stderr, "%u ", probability->dct_coeff_probs[0][0][0][k]);
-		fprintf(stderr, "\n");
-		fprintf(stderr, "vp8: VAAPI-src probability size=%zu ptr=%p\n",
-			sizeof(*probability), (void *)probability);
-		(void)p;
-	}
-
 	/* Clause 1+10: single-control batched submission */
 	struct v4l2_ext_control ctrls[1] = {
 		{