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>

libyubikey.spec

@@ -7,7 +7,6 @@ Group:          Development/Libraries
 License:        BSD
 URL:            http://opensource.yubico.com/yubico-c
 Source0:        http://opensource.yubico.com/yubico-c/releases/%{name}-%{version}.tar.gz
-BuildRoot:      %{mktemp -ud %{_tmppath}/%{name}-%{version}-%{release}-XXXXXX}
 
 %description
 This package holds a low-level C software development kit for the Yubico