tdf#42949 Fix IWYU warnings in include/salhelper/*

Found with bin/find-unneeded-includes
Only removal proposals are dealt with here.

Change-Id: Iaef3e980a96e8a831458e42540795b922bec5ab4
Reviewed-on: https://gerrit.libreoffice.org/58810
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

include/salhelper/condition.hxx

@@ -23,9 +23,10 @@
 
 
 #include "osl/conditn.hxx"
-#include "osl/mutex.hxx"
 #include "salhelper/salhelperdllapi.h"
 
+namespace osl { class Mutex; }
+
 namespace salhelper
 {
     class ConditionModifier;

include/salhelper/refobj.hxx

@@ -24,7 +24,6 @@
 
 #include "sal/types.h"
 #include "rtl/alloc.h"
-#include "osl/diagnose.h"
 #include "osl/interlck.h"
 
 namespace salhelper

salhelper/source/condition.cxx

@@ -20,7 +20,7 @@
 
 #include <salhelper/condition.hxx>
 #include <osl/time.h>
-
+#include <osl/mutex.hxx>
 
 using namespace salhelper;