perf(encode/nvenc-linux): drop the bring-up probe left on the per-frame blend path

`33121ece` added a block explicitly labelled "TEMP KWin composite probe (DROP BEFORE
MERGE)" to prove the cursor blend was dispatching. It merged, and has been running on
every blended frame since: an atomic fetch_add per frame plus a `tracing::info!` with
seven computed fields every 512 frames, on the submit hot path of the default-on
Linux direct-NVENC backend.

The signal it existed for is already covered — the failure arm above it warns once
with the dispatch error, and the `else` arm warns when an overlay arrives with no
blend at all. What is deleted is only the success-path telemetry.

Verified `-D warnings --all-targets` + tests on Linux (default; shipped
nvenc,vulkan-encode,pyrowave), and `clippy --features vulkan-encode,pyrowave` on real
AMD RDNA3 hardware.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/pf-encode/src/enc/linux/nvenc_cuda.rs

@@ -1636,25 +1636,6 @@ impl Encoder for NvencCudaEncoder {
                     }
                 } else {
                     self.cursor_blend_warned = false;
-                    // TEMP KWin composite probe (DROP BEFORE MERGE): prove the blend dispatches
-                    // and with what geometry.
-                    {
-                        use std::sync::atomic::{AtomicU64, Ordering as ProbeOrd};
-                        static PROBE_BLEND: AtomicU64 = AtomicU64::new(0);
-                        let n = PROBE_BLEND.fetch_add(1, ProbeOrd::Relaxed) + 1;
-                        if n == 1 || n % 512 == 0 {
-                            tracing::info!(
-                                n,
-                                fmt = ?self.buffer_fmt,
-                                ov_x = ov.x,
-                                ov_y = ov.y,
-                                ov_w = ov.w,
-                                ov_h = ov.h,
-                                visible = ov.visible,
-                                "cursor blend probe: vulkan dispatch submitted"
-                            );
-                        }
-                    }
                 }
             } else if !self.cursor_blend_warned {
                 self.cursor_blend_warned = true;