Stop using deprecated nodejs16 runtime. (#8159)

Author: taeold

scripts/functions-discover-tests/fixtures/codebases/firebase.json

@@ -3,7 +3,6 @@
     {
       "source": "v1",
       "codebase": "v1",
-      "runtime": "nodejs16",
       "ignore": [
         "node_modules",
         ".git",
@@ -14,7 +13,6 @@
     {
       "source": "v2",
       "codebase": "v2",
-      "runtime": "nodejs16",
       "ignore": [
         "node_modules",
         ".git",
@@ -23,4 +21,4 @@
       ]
     }
   ]
-}
+}