Merge pull request #1253 from rylev/make-syn-stable

Move syn from primary-and-stable to stable

Author: nnethercote

collector/benchmarks/syn/perf-config.json

@@ -1,4 +1,4 @@
 {
     "touch_file": "src/lib.rs",
-    "category": "primary-and-stable"
-}
+    "category": "stable"
+}