solarized-theme.el: only require `solarized' not the theme libraries

Doing so would cause both themes to be loaded, then `zenburn-theme.el` is loaded (why would one do that?) or when it is byte-compiled.

I don't know why you were loading these to libraries, maybe that is required depending on how a user activates the theme. I doubt it though, and if it were so then that would need fixing. I guess that `zenburn-theme.el` only exists to pacify Melpa/package.el, in which case it would have to contain nothing but the provide form (a library header would be nice though).