build: simplify nlohmann-json subproject

The phosphor-pid-control repository uses both phosphor-logging and
phosphor-host-ipmid as subprojects, but the way they incorporate
nlohmann-json is different.  Simplify the phosphor-logging one to
match what is available in phosphor-host-ipmid so that they can both be
build a subprojects within a single top-level project.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3484d9ee9697900dbe5e8e1895ea9d477485553d
diff --git a/subprojects/nlohmann-json.wrap b/subprojects/nlohmann-json.wrap
index 9096612..a2884b1 100644
--- a/subprojects/nlohmann-json.wrap
+++ b/subprojects/nlohmann-json.wrap
@@ -1,3 +1,6 @@
 [wrap-git]
-url = https://github.com/nlohmann/json.git
+url = https://github.com/nlohmann/json
 revision = HEAD
+
+[provide]
+nlohmann-json = nlohmann_json_dep