Remove development file

Since libslopy is considered private, there should not be need for
header file.

slop.spec.in

 %make_install
 mkdir -p "%{buildroot}%{_libdir}/slop"
 mv %{buildroot}/usr/lib/libslopy.so "%{buildroot}%{_libdir}/slop"
+rm %{buildroot}/usr/include/slop.hpp
 
 %files
 %{_bindir}/slop
-/usr/include/slop.hpp
 %{_libdir}/slop/libslopy.so
 %{_mandir}/man1/slop.1.gz