Revert "Tidy up calls to post()"

This reverts commit 5eaa2be85e.

include/boost/beast/http/impl/write.ipp

@@ -140,6 +140,7 @@ operator()()
         {
             BOOST_ASSERT(! f.invoked);
             return boost::asio::post(
+                s_.get_executor(),
                 bind_handler(std::move(*this), ec, 0));
         }
         if(f.invoked)
@@ -152,6 +153,7 @@ operator()()
         BOOST_ASSERT(sr_.is_done());
     }
     return boost::asio::post(
+        s_.get_executor(),
         bind_handler(std::move(*this), ec, 0));
 }
 
@@ -282,6 +284,7 @@ operator()(
         {
             state_ = 1;
             return boost::asio::post(
+                s_.get_executor(),
                 bind_handler(std::move(*this), ec, 0));
         }
         state_ = 2;