Revert "temp: pin boto3 to 1.34.115"

[timmc-edx]

Reverts #22 -- should no longer be needed.

See edx/edx-arch-experiments#668

The error we had been seeing:

:stderr: ERROR: Could not find a version that satisfies the requirement botocore<1.35.0,>=1.34.116 (from boto3) (from versions: 0.4.1, ..., 1.34.115)

From discussion about reverting the pin:

I suspect this will work because boto3/botocore 1.34.116 was just released, and there's probably a stale index not allowing the botocore dependency to be fetched. (boto3 requires the most recent botocore.)