src: do not shrink async resources on every pop

AsyncHooks::pop_async_context() calls shrink_to_fit() on
native_execution_async_resources_ after every pop. With the MSVC and
libc++ standard libraries, shrink_to_fit() on an empty std::deque frees
its storage, so every top-level callback scope allocates it again on
push and frees it on pop. libstdc++ does nothing here.

A program with the same pattern, a std::deque of the same variant going
from 0 to 1 to 0 elements, takes 136-147 ns per callback on Windows
with MSVC, and 6 ns without shrink_to_fit(). The async_ids_stack_ next
to it never shrinks either.

Refs: nodejs/performance#24
Signed-off-by: Nigro Simone <nigro.simone@gmail.com>

Author: nigrosimone

src/env.cc

@@ -196,7 +196,6 @@ bool AsyncHooks::pop_async_context(double async_id) {
     }
 #endif
     native_execution_async_resources_.resize(offset);
-    native_execution_async_resources_.shrink_to_fit();
   }
 
   if (js_execution_async_resources()->Length() > offset) [[unlikely]] {