meson: adjust nlohmann-json dependency

Simplify the nlohmann-json dependency and align the wrap file with other
repositories.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic41132c20f48da7591ff380b3448ab73fa78052b
diff --git a/meson.build b/meson.build
index 6593b3d..741347b 100644
--- a/meson.build
+++ b/meson.build
@@ -23,17 +23,6 @@
   language: 'cpp',
 )
 
-if cpp.has_header('nlohmann/json.hpp')
-    nlohmann_json_dep = declare_dependency()
-else
-    subproject('nlohmann-json')
-    nlohmann_json_dep = declare_dependency(
-        include_directories: include_directories(
-            'subprojects/nlohmann-json/single_include',
-            'subprojects/nlohmann-json/single_include/nlohmann',
-        )
-    )
-endif
 
 boost_dep = dependency(
   'boost',
@@ -41,6 +30,7 @@
   include_type: 'system',
 )
 i2c_dep = cpp.find_library('i2c')
+nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
 phosphor_logging_dep = dependency('phosphor-logging')
 sdbusplus_dep = dependency('sdbusplus')
 systemd_dep = dependency('systemd')