meson: adjust nlohmann-json dependency

Simplify meson dependency logic and align wrap file name with other
repositories.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I516b4155786e4ae2d72c99e3e253c63db3752449
diff --git a/meson.build b/meson.build
index f73b214..67442b5 100644
--- a/meson.build
+++ b/meson.build
@@ -119,14 +119,7 @@
 sdbusplus_dep = dependency('sdbusplus')
 stdplus_dep = dependency('stdplus')
 
-if cpp.has_header_symbol(
-        'nlohmann/json.hpp',
-        'nlohmann::json::string_t',
-        required:false)
-    nlohmann_json_dep = declare_dependency()
-else
-    nlohmann_json_dep = dependency('nlohmann-json')
-endif
+nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
 
 generated_src = []