[apis] trim supported branch list

Author: spalger

package.json

@@ -29,21 +29,11 @@
     "blanket": {
       "pattern": "specified in test/unit/coverage.js"
     },
-    "default_api_branch": "6.7",
+    "default_api_branch": "7.0",
     "supported_es_branches": [
       "7.0",
       "6.7",
-      "6.6",
-      "6.5",
-      "6.4",
-      "6.3",
-      "6.2",
-      "6.1",
-      "6.0",
-      "5.6",
-      "2.4",
-      "1.7",
-      "0.90"
+      "5.6"
     ],
     "unstable_es_branches": [
       "6.8",