Remove BuildRoot definition

None of currently supported distributions need that.
It was needed last for EL5 which is EOL now

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

libgdither.spec

@@ -9,7 +9,6 @@ URL:            http://plugin.org.uk/libgdither/README
 Source0:        http://plugin.org.uk/libgdither/libgdither-%{version}.tar.gz
 Patch0:         libgdither-0.6-default.patch
 Patch1:         libgdither-0.6-gavl.patch
-BuildRoot:      %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
 
 BuildRequires:  fftw-devel >= 3.0.0