CLN: Cython warnings for type declartions
```
warning: pandas/_libs/internals.pyx:144:29: Strings should no longer be used for type declarations. Use 'cython.int' etc. directly.
warning: pandas/_libs/internals.pyx:147:32: Strings should no longer be used for type declarations. Use 'cython.int' etc. directly.
warning: pandas/_libs/internals.pyx:188:28: Strings should no longer be used for type declarations. Use 'cython.int' etc. directly.
```
(Against cython master)

