remove redundant experiment (#76)

diff --git a/analysis_options.yaml b/analysis_options.yaml
index 2036951..29ad479 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -6,6 +6,3 @@
 # including a list of lints that are intentionally _not_ enforced.
 
 include: lib/analysis_options.yaml
-analyzer:
-  enable-experiment:
-    - non-nullable