DEPS: Bump minimum Numba version
xref https://github.com/pandas-dev/pandas/pull/43172#discussion_r697458641

The current min version is 0.46.0 which came out 2019-10-10.

Bumping to at least 0.49.0 (which came out 2020-04-17) would allow this version check to be removed:

https://github.com/pandas-dev/pandas/blob/b9e90dc8acf003588678196e7dc8294114918bb2/pandas/core/util/numba_.py#L90

