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>

arj.spec

@@ -26,7 +26,6 @@ Patch12:        arj-3.10.22-security-traversal-symlink.patch
 BuildRequires:	autoconf
 Provides:	unarj = %{version}-%{release}
 Obsoletes:	unarj < 3
-BuildRoot:	%{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
 
 %description
 This package is an open source version of the arj archiver. It has