update the analysis_options.yaml file (#449)

diff --git a/analysis_options.yaml b/analysis_options.yaml
index 4cce960..d18178b 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,7 +1,4 @@
 analyzer:
-  enable-experiment:
-  - non-nullable
-
   language:
     strict-raw-types: true