Tidy up comment referring to hash
Update db/structure.sql to remove path_hash columns

This is dumped from Transition's database in dev, as usual. That dump
also wanted to remove the following line, but I haven't included that
change in this commit:

SET lock_timeout = 0;
Merge pull request #108 from alphagov/update_db_structure_without_path_hash

Update db/structure.sql to remove path_hash columns
Merge pull request #109 from alphagov/remove-path-hash-references

Tidy up comment referring to hash