remove unused `#generalized_table`

This method was copied from journey at https://github.com/rails/rails/commit/56fee39c392788314c44a575b3fd66e16a50c8b5#diff-d89de8881fc4b9f10cb3e4fc7b2463f3R53. However it looks the method was unused in journey at those point as well.

`grep -nr 'generalized_table' .`

To find other potentially methods in ruby projects you can use the gem _cleanup_ from https://github.com/QFocusLabs/cleanup.