Remove an unnecessary step from codeql.yml (#254)

Signed-off-by: Sora Morimoto <sora@morimoto.io>

.github/workflows/codeql.yml

@@ -1,4 +1,4 @@
-name: "Code scanning"
+name: 'Code scanning'
 
 on:
   push:
@@ -8,24 +8,11 @@ on:
 
 jobs:
   CodeQL-Build:
-
-    # CodeQL runs on ubuntu-latest and windows-latest
     runs-on: ubuntu-latest
-
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2
-      with:
-        # We must fetch at least the immediate parents so that if this is
-        # a pull request then we can checkout the head.
-        fetch-depth: 2
 
-    # If this run was triggered by a pull request event, then checkout
-    # the head of the pull request instead of the merge commit.
-    - run: git checkout HEAD^2
-      if: ${{ github.event_name == 'pull_request' }}
-      
-    # Initializes the CodeQL tools for scanning.
       - name: Initialize CodeQL
         uses: github/codeql-action/init@v1