Delete cache.rst

CacheHelper has been removed in 6441e418dde28e263890923358882be8eb2ae159
cakephp/cakephp@6441e41

remove cacheHelper link
Merge pull request #1511 from antograssiot/3.0

CacheHelper reference removal
Removed not needed 'to' in ORM migration and changed 'object' to 'objects' in ORM
Removed not needed 'to' in ORM migration and changed 'object' to 'objects' in ORM
Merge branch '3.0' of github.com:amitrb/docs into 3.0
Merge pull request #1515 from amitrb/3.0

Removed not needed 'to' in ORM migration and changed 'object' to 'objects' in ORM
Fixed minor typos for ORM's query builder
Merge pull request #1516 from amitrb/3.0

Fixed minor typos for ORM's query builder