Remove docs requirement install
Remove docs requirement install

Problem: Docs requirements are not needed; containthedocs can be used instead. The docs req file doesn't exist,
but the devel image dockerfile attempts to install it.

Solution: Remove the docs install step in the devel-image, as the docs requirements file no longer exists.

michaeldayreads/marathon-bigip-ctlr,michaeldayreads/marathon-bigip-ctlr,michaeldayreads/marathon-bigip-ctlr