Clarify ASYNC_WAIT_CTX_clear_fd() docs

Clarify that the "cleanup" routing does not get called if you invoke
ASYNC_WAIT_CTX_clear_fd() directly.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

crypto/async/async_wait.c

@@ -191,7 +191,8 @@ int ASYNC_WAIT_CTX_clear_fd(ASYNC_WAIT_CTX *ctx, const void *key)
         if (curr->key == key) {
             /*
              * Mark it as deleted. We don't call cleanup if explicitly asked
-             * to clear an fd. We assume the caller is going to do that
+             * to clear an fd. We assume the caller is going to do that (if
+             * appropriate).
              */
             curr->del = 1;
             ctx->numdel++;

doc/crypto/ASYNC_WAIT_CTX_new.pod

@@ -90,7 +90,8 @@ in a subsequent call to ASYNC_WAIT_CTX_get_fd(). The
 ASYNC_WAIT_CTX_set_wait_fd() function also expects a pointer to a "cleanup"
 routine. This can be NULL but if provided will automatically get called when the
 ASYNC_WAIT_CTX is freed, and gives the engine the opportunity to close the fd or
-any other resources.
+any other resources. Note: The "cleanup" routine does not get called if the fd
+is cleared directly via a call to ASYNC_WAIT_CTX_clear_fd().
 
 An example of typical usage might be an async capable engine. User code would
 initiate cryptographic operations. The engine would initiate those operations