Remove DO_NO_STD from fuzz job

Use of `DO_FUZZ` causes `test.sh` to exit immediately after fuzzing,
therefore the `DO_NO_STD` option is meaningless, remove it to prevent
confusion.

Author: tcharding

.github/workflows/rust.yml

@@ -24,7 +24,6 @@ jobs:
       - name: Running fuzzer
         env:
           DO_FUZZ: true
-          DO_NO_STD: true
         run: ./contrib/test.sh
 
   Nightly: