docs: use default timeout for restore operation (#1109)

The restore operation should use the default timeout of a restore operation.
Although that timeout is long, the tests for the samples are only executed as
part of the nightly build, which means that a long-running restore will not
slow down PR builds.

Fixes #1019

samples/snippets/src/main/java/com/example/spanner/RestoreBackupWithEncryptionKey.java

@@ -30,8 +30,6 @@
 import com.google.cloud.spanner.encryption.EncryptionConfigs;
 import com.google.spanner.admin.database.v1.RestoreDatabaseMetadata;
 import java.util.concurrent.ExecutionException;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
 
 public class RestoreBackupWithEncryptionKey {
 
@@ -71,17 +69,14 @@ static Void restoreBackupWithEncryptionKey(DatabaseAdminClient adminClient,
     Database database;
     try {
       System.out.println("Waiting for operation to complete...");
-      database = operation.get(1600, TimeUnit.SECONDS);
+      database = operation.get();
     } catch (ExecutionException e) {
       // If the operation failed during execution, expose the cause.
       throw SpannerExceptionFactory.asSpannerException(e.getCause());
     } catch (InterruptedException e) {
       // Throw when a thread is waiting, sleeping, or otherwise occupied,
       // and the thread is interrupted, either before or during the activity.
       throw SpannerExceptionFactory.propagateInterrupt(e);
-    } catch (TimeoutException e) {
-      // If the operation timed out propagates the timeout
-      throw SpannerExceptionFactory.propagateTimeout(e);
     }
 
     System.out.printf(