ci: drop unnecessary protoc installs

[abnobdoss]

Which issue does this PR close?

• None. CI maintenance.

What changes are included in this PR?

Deletes every Install protoc step: five in ci.yml, one in public-api.yml, one in website.yml.

The installs were added with the datafusion 48 bump (#1501). That bump pulled in the substrait crate, whose build script runs prost-build, and prost-build shells out to protoc. The DataFusion 54 bump (#2648) dropped substrait and prost-build from the tree, and prost-build was the only thing that ever ran protoc. The remaining prost/prost-derive dependencies come from datafusion-proto, which ships pregenerated code and has no build script. So nothing in make build, the test suite, or the cargo doc run in website.yml needs protoc anymore.

A side benefit of this simplification is that we remove a dependency on arduino/setup-protoc, which hasn't seen a commit since September 2024 and was printing a Node runtime deprecation warning on every run.

Are these changes tested?

• Verified on a fork based past chore(deps): Bump DataFusion to 54.0.0 #2648: all ci.yml and public-api.yml jobs run green without protoc, including the full docker-backed test suite.
• cargo metadata confirms datafusion-proto and datafusion-proto-common have no build script. prost-build is absent from Cargo.lock and nothing in the workspace source references protoc.