Remove nlohmann brace initialization

There's a few last places (outside of tests) where we still use
nlohmann brace initialization.  Per the transforms we've been doing,
move these to constructing the objects explicitly, using operator[],
nlohmann::object_t and nlohmann::array_t.  Theses were found by manual
inspection grepping for all uses of nlohmann::json.

This is done to reduce binary size and reduce the number of intermediate
objects being constructed.  This commit saves a trivial amount of size
(~4KB, Half a percent of total) and in addition but makes our
construction consistent.

Tested:
Redfish service validator passes.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I7478479a9fdc41b254eef325002d413c1fb411a0
diff --git a/redfish-core/lib/virtual_media.hpp b/redfish-core/lib/virtual_media.hpp
index 15dcdb9..af38163 100644
--- a/redfish-core/lib/virtual_media.hpp
+++ b/redfish-core/lib/virtual_media.hpp
@@ -155,7 +155,7 @@
     item["Name"] = "Virtual Removable Media";
     item["Id"] = resName;
     item["WriteProtected"] = true;
-    item["MediaTypes"] = {"CD", "USBStick"};
+    item["MediaTypes"] = nlohmann::json::array_t({"CD", "USBStick"});
     item["TransferMethod"] = "Stream";
     item["Oem"]["OpenBMC"]["@odata.type"] =
         "#OemVirtualMedia.v1_0_0.VirtualMedia";