Remove references to submodules (#11673)

This PR removes the references to initializing Git submodules as part of
building Zed.

These are no longer needed, as our only submodule was removed in #11672.

Release Notes:

- N/A

.github/workflows/release_nightly.yml

@@ -25,7 +25,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           clean: false
-          submodules: "recursive"
           fetch-depth: 0
 
       - name: Run style checks
@@ -45,7 +44,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           clean: false
-          submodules: "recursive"
 
       - name: Run tests
         uses: ./.github/actions/run_tests
@@ -75,7 +73,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           clean: false
-          submodules: "recursive"
 
       - name: Set release channel to nightly
         run: |
@@ -109,7 +106,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           clean: false
-          submodules: "recursive"
 
       - name: Add Rust to the PATH
         run: echo "$HOME/.cargo/bin" >> $GITHUB_PATH