remove redundant experiment (dart-lang/term_glyph#20)

pkgs/term_glyph/analysis_options.yaml

diff --git a/pkgs/term_glyph/analysis_options.yaml b/pkgs/term_glyph/analysis_options.yaml
index 64ff556..108d105 100644
--- a/pkgs/term_glyph/analysis_options.yaml
+++ b/pkgs/term_glyph/analysis_options.yaml
@@ -1,4 +1 @@
 include: package:pedantic/analysis_options.yaml
-analyzer:
-  enable-experiment:
-    - non-nullable