How to find all inputs that make use of the php input filter to fully disable the php filter module?
Rather than re-inventing the wheel, just install the Security Review module, which has the following check:


  PHP or Javascript in content (nodes and comments and fields in Drupal 7)


For blocks you can check the format column in the block_custom table.

The difficult one is Views - I've yet to find a reliable way to locate rogue PHP in Views programmatically.