Revert "BUG: fix python 2.5."

This reverts commit 3ed7eb4dc9599c27eaea868cb0863162b4eae51f.
Revert "MAINT: add 2.5 in travis-ci."

This reverts commit 717fc0bde626cfe92964a0cd4cb6d7eb69867145.
Revert "MAINT: let's add 2.5 as well."

This reverts commit 5a6dc5467a04666b7cfa2b00efa43c8147957804.