bmcweb: Remove deprecatd ASIO interfaces

boost::asio::io_service is removed in leiu of io_context, which is a
closer match to the networking TS.  Move us to that implementatio.

This was an automated move using the following command:
git grep -l 'io_service' | xargs sed -i 's/io_service/io_context/g'

Change-Id: I46605521c01f79f86f6901ddf69ddc8c4bc24103
Signed-off-by: Ed Tanous <ed.tanous@intel.com>
diff --git a/src/webassets_test.cpp b/src/webassets_test.cpp
index a3106f2..3df7542 100644
--- a/src/webassets_test.cpp
+++ b/src/webassets_test.cpp
@@ -25,7 +25,7 @@
     // get the homepage
     std::string sendmsg = "GET /\r\n\r\n";
 
-    asio::io_service is;
+    asio::io_context is;
 
     asio::ip::tcp::socket c(is);
     c.connect(asio::ip::tcp::endpoint(
@@ -100,7 +100,7 @@
     // get the homepage
     std::string sendmsg = "GET /\r\n\r\n";
 
-    asio::io_service is;
+    asio::io_context is;
 
     asio::ip::tcp::socket c(is);
     c.connect(asio::ip::tcp::endpoint(