Remove numpy pin from environment.yml on 1.2.x
xref #39513, expected to fail until #39994 backported

This PR is directly against 1.2.x and ignores site packages for mypy checks.
can remove blocker label from #39513 on merge, https://github.com/pandas-dev/pandas/issues/39513#issuecomment-771006563 > expected to fail until #39994 backported

the problematic benchmark is only on master lgtm. @simonjayhawkins merge when ready