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>

libesmtp.spec

@@ -8,7 +8,6 @@ License:        LGPLv2+
 Group:          System Environment/Libraries
 Source:         http://www.stafford.uklinux.net/libesmtp/%{name}-%{version}.tar.bz2
 URL:            http://www.stafford.uklinux.net/libesmtp/
-BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
 BuildRequires:  openssl-devel pkgconfig
 
 %description