meson: Clean up specification of liburing dependency

The manual attempt at handling a fallback is unnecessary - let meson do
the work for us in the idiomatic way of deferring to a wrap of the same
name.

Change-Id: Iffe648e3edfa9155a7652e323f04cf762f1b0bf4
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/meson.build b/meson.build
index d50c7e3..334f01e 100644
--- a/meson.build
+++ b/meson.build
@@ -69,12 +69,7 @@
     boost = boost.as_system('system')
 endif
 
-uring = dependency('liburing', required: false, include_type: 'system')
-if not uring.found()
-    uring_proj = subproject('liburing', required: true)
-    uring = uring_proj.get_variable('uring')
-    uring = uring.as_system('system')
-endif
+uring = dependency('liburing', include_type: 'system')
 
 default_deps = [
     boost,