Revert "[kennethreitz/requests#1208] adding a max_retries argument"

This reverts commit 796d3225ddf08a9ebaa429209b9d077c3a8f99b8.
Revert "[kennethreitz/requests#1208] adding unit test for max_retries"

This reverts commit 18b29ea00563a0bf8e15666806117444c87ac23f.