Remove default_nettype statements at the end of the RTL

[kareefardi]

Surfaced by https://github.com/The-OpenROAD-Project/OpenLane/issues/2083. Yosys would use the default nettype wire when compiling the user project. Although this might be an ambiguity in yosys behavior, I don't see the need of adding these lines. Having said that, there presence in the RTL seems to be intentional, I added @marwaneltoukhy and @M0stafaRady as reviewers to asses if this PR is going to have any further impact.