hooks: strip: move to post-install to generate shlib-provides for all pkgs.

That was the missing piece to generate proper dependencies in 32bit
packages with subpkgs that depended in other subpkgs.

For example kmod: libkmod and libkmod-devel. libkmod-devel was being processed
before libkmod, and due to missing shlib-provides a dependency to the 64bit
package was generated.