Fix few issues according to fedora packaging guidelines

* Package does not run rm -rf %{buildroot} (or $RPM_BUILD_ROOT) at the
     beginning of %install.
* Buildroot is not present
     Note: Buildroot: present but not needed
* Package has no %clean section with rm -rf %{buildroot} (or
             $RPM_BUILD_ROOT)
     Note: %clean present but not required

libtevent.spec

@@ -14,7 +14,6 @@ Summary: The tevent library
 License: LGPLv3+
 URL: http://tevent.samba.org/
 Source: http://samba.org/ftp/tevent/tevent-%{version}.tar.gz
-BuildRoot: %(mktemp -ud %{_tmppath}/%{name}-%{version}-%{release}-XXXXXX)
 
 BuildRequires: libtalloc-devel >= 2.0.7
 BuildRequires: python-devel
@@ -109,7 +108,6 @@ make %{?_smp_mflags} V=1
 doxygen doxy.config
 
 %install
-rm -rf $RPM_BUILD_ROOT
 
 make install DESTDIR=$RPM_BUILD_ROOT
 
@@ -124,9 +122,6 @@ rm -f doc/man/man3/todo*
 mkdir -p $RPM_BUILD_ROOT/%{_mandir}
 cp -a doc/man/* $RPM_BUILD_ROOT/%{_mandir}
 
-%clean
-rm -rf $RPM_BUILD_ROOT
-
 %files
 %defattr(-,root,root,-)
 %{_libdir}/libtevent.so.*