At 1.6 release: update ConanCenter recipe (signed tarball, drop patch)

Checklist for the ConanCenter (`conan-io/conan-center-index`) version bump when 1.6 is released, capturing follow-ups from this cycle's packaging work (#238/#246, #249, #253):

- [ ] Run (or confirm auto-run of) the **Sign Release** workflow on the 1.6 tag, producing `openfx-1.6.tar.gz`, `.sigstore.json`, and `.sha256` release assets (#249).
- [ ] Open a CCI PR adding 1.6 to `recipes/openfx/config.yml` and `all/conandata.yml`. Point `conandata.yml` at the **signed release-asset tarball URL** (immutable, verifiable), not the auto-generated `archive/refs/tags/...` URL, using the checksum from the `.sha256` asset.
- [ ] **Delete `all/patches/1.5.1-0001-disable-example-requirements.patch`** for the new version: the install rules were upstreamed in #246 and the example-only dependency trimming in #253, so the 1.6 tree should need no patching. Verify with a local `conan create` from the CCI recipe.
- [ ] Sanity-check remaining recipe deltas against the in-repo `conanfile.py` (CMake module path `lib/cmake/OpenFX/` vs `lib/cmake/`, license subdir) and reconcile or document as intentional.

Also verify the in-repo version single-sourcing (CMakeLists `project()` VERSION) is bumped to 1.6 as part of the release itself.

Start with the Sign Release workflow and the in-repo CMakeLists.txt to confirm the 1.6 release assets and project version. Then compare recipes/openfx/config.yml, all/conandata.yml, all/patches/1.5.1-0001-disable-example-requirements.patch, and conanfile.py with the ConanCenter recipe. Done means a signed, checksummed tarball is referenced, the obsolete patch is removed, recipe deltas are reconciled, and a local conan create succeeds.

Written by the indexing model from the issue text.