test: Remove unused scheduler.h include from the common setup

The common setup is included in virtually all tests, so it should be
as slim as possible.

src/test/util/setup_common.cpp

@@ -19,6 +19,7 @@
 #include <rpc/blockchain.h>
 #include <rpc/register.h>
 #include <rpc/server.h>
+#include <scheduler.h>
 #include <script/sigcache.h>
 #include <streams.h>
 #include <txdb.h>