IWYU: drop some exceptions related to rtl::math and std::

at least recent 0.24 no longer warns about these

Change-Id: I1f7c4069df7d47bcd720298c93d71fd6c7bbed9b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/191002
Reviewed-by: Gabor Kelemen <gabor.kelemen.extern@allotropia.de>
Tested-by: Jenkins

forms/IwyuFilter_forms.yaml

@@ -30,9 +30,6 @@ excludelist:
     forms/source/component/imgprod.cxx:
     # Actually used
     - com/sun/star/io/XInputStream.hpp
-    forms/source/component/scrollbar.cxx:
-    # Needed for rtl::math::round
-    - rtl/math.hxx
     forms/source/richtext/parametrizedattributedispatcher.cxx:
     # Actually used
     - com/sun/star/beans/PropertyValue.hpp