Remove ExecutorService from BspClient, since it was used for extracting line offset from generated sources, with the current implementation we don't read the files so no need for more threads.

Original code's purpose can be seen in the commit that introduces it: 4297b07.

Author: MaciejG604

modules/build/src/main/scala/scala/build/bsp/BspImpl.scala

@@ -454,7 +454,7 @@ final class BspImpl(
     * @param initialInputs
     *   the initial input sources passed upon initializing the BSP connection (which are subject to
     *   change on subsequent workspace/reload requests)
-    */
+   */
   override def run(initialInputs: Inputs, initialBspOptions: BspReloadableOptions): Future[Unit] = {
     val logger    = initialBspOptions.logger
     val verbosity = initialBspOptions.verbosity