Revert "THRIFT-4951: Remove senum from tests"

This reverts commit df8ef4b489e2b84ac6dbbf895be32d6fb2415c81.

The contributor confuses "deprecated" with "unsupported". Unless the feature as a whole is also removed, so essentially nothing is left to be tested. Regardless whether a particular feature is deprecated or not, removing a working test for it is NOT helpful. The only "achievement" of such efforts would be that the test coverage goes down, which is clearly not in our intention and only opens room for bugs and issues.
diff --git a/test/AnnotationTest.thrift b/test/AnnotationTest.thrift
index 6238395..7e24e1c 100644
--- a/test/AnnotationTest.thrift
+++ b/test/AnnotationTest.thrift
@@ -49,6 +49,14 @@
   SATURDAY ( weekend = "yes" )
 } (foo.bar="baz")
 
+/* Note that annotations on senum values are not supported. */
+senum seasons {
+  "Spring",
+  "Summer",
+  "Fall",
+  "Winter"
+} ( foo = "bar" )
+
 struct ostr_default {
   1: i32 bar;
 }