ci: Remove unnecessary performance-impact job from PR validation

- Remove performance impact analysis job from pr-validation workflow
- Simplifies PR validation by focusing on essential checks only
- Reduces CI execution time and resource usage

The performance benchmarking was not providing actionable insights
and added complexity without significant value to the validation process.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: fummicc1

.github/workflows/pr-validation.yml

@@ -160,78 +160,3 @@ jobs:
         else
           echo "No Swift source files changed in this PR"
         fi
-
-  performance-impact:
-    name: Performance Impact Analysis
-    runs-on: macos-15
-    if: github.event.pull_request.draft == false
-    
-    steps:
-    - name: Checkout base branch
-      uses: actions/checkout@v4
-      with:
-        ref: ${{ github.base_ref }}
-        
-    - name: Setup Xcode
-      uses: maxim-lobanov/setup-xcode@v1
-      with:
-        xcode-version: '16.4'
-        
-    - name: Setup Swift
-      run: |
-        # macOS - use Xcode's Swift
-        echo "Using Xcode's Swift on macOS"
-        xcode-select --print-path
-        swift --version
-        
-    - name: Build baseline
-      run: |
-        swift build --configuration release
-        
-    - name: Benchmark baseline
-      run: |
-        # Create a sample Swift file for benchmarking
-        mkdir -p benchmark-data
-        cat > benchmark-data/sample.swift << 'EOF'
-        func complexFunction(param: Int) -> String {
-            if param > 100 {
-                for i in 0..<param {
-                    if i % 2 == 0 {
-                        if i % 4 == 0 {
-                            print("Complex logic")
-                        }
-                    }
-                }
-                return "high"
-            } else if param > 50 {
-                return "medium"
-            } else {
-                return "low"
-            }
-        }
-        EOF
-        
-        # Benchmark the current version
-        time swift run swift-complexity benchmark-data/sample.swift --format json > baseline-benchmark.json
-        
-    - name: Checkout PR
-      uses: actions/checkout@v4
-      with:
-        ref: ${{ github.event.pull_request.head.sha }}
-        
-    - name: Build PR version
-      run: |
-        swift build --configuration release
-        
-    - name: Benchmark PR version
-      run: |
-        # Benchmark the PR version
-        time swift run swift-complexity benchmark-data/sample.swift --format json > pr-benchmark.json
-        
-    - name: Compare results
-      run: |
-        echo "Baseline benchmark completed"
-        echo "PR benchmark completed"
-        echo "Performance comparison would be implemented here"
-        # In a real scenario, you'd compare execution times and memory usage
-