MAINT: Revert "BUG: do a boolean check on casting bool to other types"

This reverts commit cf13331897acb84d0a6a118c6ba4d700905d3e3e for the
1.8.0 release. The scikit-image package makes unwarrented use of the
numpy boolean type that results in some bugs when boolean values of 0, 1
are enforced. This reversion avoids exposing those bugs and provide the
skimage developers some time to set things right.
Merge pull request #3853 from charris/skimage-fix-binary

Skimage fix binary