Remove mentions of submodules from the docs

Author: OlivierBlanvillain

.drone.yml

@@ -16,7 +16,7 @@ pipeline:
           git config user.name "Dotty CI";
           git pull "$DRONE_REMOTE_URL" "$DRONE_BRANCH";
         fi
-      # clone submodules in parallelRiRem
+      # clone submodules in parallel
       - git submodule update --init --recursive --jobs 3
 
   # TESTS:

docs/docs/contributing/getting-started.md

@@ -15,15 +15,11 @@ Compiling and Running
 Start by cloning the repository:
 
 ```bash
-$ git clone --recurse-submodules --single-branch https://github.com/lampepfl/dotty.git
+$ git clone https://github.com/lampepfl/dotty.git
 $ cd dotty
 $ sbt managedSources # Needed for IDE import to succeed
 ```
 
-Pass `--single-branch` to clone only the master branch, otherwise cloning will be *much* slower (details in [issue #3236](https://github.com/lampepfl/dotty/issues/3236)).
-
-The repository uses submodules, which may need updating/initializing using `git submodule update --init`. Starting `sbt` will alert you if this is needed.
-
 Dotty provides a standard sbt build: compiling, running and starting a repl can
 all be done from within sbt:
 

project/Build.scala

@@ -157,16 +157,6 @@ object Build {
         }
       }
 
-      // Make sure all submodules are properly cloned
-      val submodules = List("scala-backend", "scala2-library")
-      if (!submodules.forall(exists)) {
-        sLog.value.log(Level.Error,
-          s"""Missing some of the submodules
-             |You can initialize the modules with:
-             |  > git submodule update --init
-          """.stripMargin)
-      }
-
       // Copy default configuration from .vscode-template/ unless configuration files already exist in .vscode/
       sbt.IO.copyDirectory(new File(".vscode-template/"), new File(".vscode/"), overwrite = false)