Remove unndecessary environment variable form ava.config.js

Author: octet-stream

ava.config.js

@@ -1,6 +1,5 @@
 export default {
   environmentVariables: {
-    TS_NODE_PREFER_TS_EXTS: "true",
     SWC_NODE_PROJECT: "./tsconfig.ava.json",
     SWCRC: "true"
   },