src: remove unnecessary check

The value's type is unsigned so it will always be >= 0.

Ref: https://github.com/nodejs/node/pull/7048
PR-URL: https://github.com/nodejs/node/pull/5233
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/env-inl.h

@@ -95,7 +95,6 @@ inline Environment::AsyncCallbackScope::AsyncCallbackScope(Environment* env)
 
 inline Environment::AsyncCallbackScope::~AsyncCallbackScope() {
   env_->makecallback_cntr_--;
-  CHECK_GE(env_->makecallback_cntr_, 0);
 }
 
 inline bool Environment::AsyncCallbackScope::in_makecallback() {