Remove unused imports.

Author: vbabanin

driver-core/src/main/com/mongodb/internal/async/AsyncTrampoline.java

@@ -17,11 +17,8 @@
 package com.mongodb.internal.async;
 
 import com.mongodb.annotations.NotThreadSafe;
-import com.mongodb.assertions.Assertions;
 import com.mongodb.lang.Nullable;
 
-import static com.mongodb.assertions.Assertions.assertNotNull;
-
 /**
  * A trampoline that converts recursive callback invocations into an iterative loop,
  * preventing stack overflow in async loops.