Remove gnzlbg from libc's review queue

Author: tesuji

highfive/configs/rust-lang/libc.json

@@ -1,6 +1,6 @@
 {
     "groups": {
-        "all": ["@gnzlbg", "@JohnTitor"]
+        "all": ["@JohnTitor"]
     },
     "dirs": {
     }