tdf#42949 Fix IWYU warnings in include/{store,registry}/*

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

Change-Id: I9c3561292f770795623b765b1ea2ce80b9700ada
Reviewed-on: https://gerrit.libreoffice.org/58821
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

include/IwyuFilter_include.yaml

@@ -40,3 +40,9 @@ blacklist:
     include/rtl/math.hxx:
     # TODO MSVC does not compile basegfx/numeric/ftools.hxx when this is replaced
     - math.h
+    include/registry/regtype.h:
+    # Needed for template
+    - o3tl/typed_flags_set.hxx
+    include/registry/types.hxx:
+    # Needed for template
+    - o3tl/typed_flags_set.hxx

include/store/store.hxx

@@ -22,7 +22,6 @@
 
 #include <store/store.h>
 #include <sal/types.h>
-#include <stddef.h>
 #include <rtl/ustring.hxx>
 #include <store/types.h>