Revert "ci: introduce `classify-pr.sh` script which determines whether a PR should have CI run"

This reverts commit 9aca8a18c7.

.github/workflows/rust.yml

@@ -14,13 +14,9 @@ jobs:
       crates: ${{ steps.get_matrix.outputs.crates }}
       deps: ${{ steps.get_matrix.outputs.deps }}
       nightly_version: ${{ steps.read_toolchain.outputs.nightly_version }}
-      pr_changed_source: ${{ steps.classify_pr.outputs.pr_changed_source }}
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v4
-      - name: Determine what files the PR changes.
-        id: classify_pr
-        run: contrib/classify-pr.sh ${{ github.event.pull_request.head.sha }} ${{ github.event.pull_request.base.sha }}
       - name: Read nightly version
         id: read_toolchain
         run: echo "nightly_version=$(cat .github/nightly-version)" >> $GITHUB_OUTPUT

contrib/classify-pr.sh

@@ -1,25 +0,0 @@
-#!/bin/sh
-
-if [ "$#" -ne 2 ]; then
-  echo "Usage: $0 <tip of master> <tip of PR>"
-  exit 1
-fi
-
-pr_tip=$1
-master_tip=$2
-
-# When called on `pull_request`, GA fails to pull down master by default.
-# When called on `push`, GA fails to pull down the PR by default, only its merge commit.
-# The simplest way to deal with this is to just pull both explicitly.
-git fetch origin "$master_tip":master_tip
-git fetch origin "$pr_tip":pr_tip
-
-pr_base=$(git merge-base master_tip pr_tip)
-
-# If something modifies any non-markdown file, it's considered a source code change.
-if git diff --name-only "$pr_base" "$pr_tip" | grep -qv "^.md$"; then
-    echo "pr_changed_source=true" >> "$GITHUB_OUTPUT"
-else
-    echo "pr_changed_source=false" >> "$GITHUB_OUTPUT"
-fi
-