paper(gemm): drop in-chart titles + subtitles, let LaTeX caption carry that

The matplotlib title and gray subtitle were duplicating what the
figure caption already says in the LaTeX source, and crowding the
top of every chart. Drop both — chart now leaves the title/subtitle
slots blank and the caption is the single source of truth for
chart titling.

Re-render all 5 GEMM figures (mac util measured, mac util theoretical
vs measured, stage breakdown, HBM BW util, per-PE TFLOPS) and resync
into docs/report/1H-codesign-paper/figures/. No data changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/kernbench/benches/milestone_1h_gemm.py

@@ -365,15 +365,11 @@ def _grouped_bar_png(
         _xtick_labels(shape_labels, tile_counts, flagged), fontsize=8,
     )
     ax.set_ylabel(y_label)
-    # Title with optional subtitle stacked above (subtitle in lighter ink,
-    # title in bold below it). Coordinates are in axes-fraction so they
-    # survive tight_layout without colliding with the data area.
-    if subtitle:
-        ax.text(0.5, 1.10, subtitle, transform=ax.transAxes, ha="center",
-                va="bottom", fontsize=8, color="#475569")
-        ax.set_title(title, fontsize=13, fontweight="bold", pad=22)
-    else:
-        ax.set_title(title, fontsize=13, fontweight="bold")
+    # Title and subtitle are intentionally not drawn here — the LaTeX
+    # figure caption is the single source of truth for chart titling.
+    # `title` and `subtitle` parameters are kept on the signature so
+    # existing callers don't need to change.
+    del title, subtitle  # silence unused-argument linters
     if threshold is not None:
         ax.axhline(threshold, ls="--", color="gray", lw=1.0)
     ax.legend(fontsize=8, loc="upper right")