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Remove openfst, imported to math/openfst.

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Import openfst-1.1 as wip/openfst.

OpenFst is a library for constructing, combining, optimizing, and searching
weighted finite-state transducers (FSTs). Weighted finite-state transducers are
automata where each transition has an input label, an output label, and a
weight. The more familiar finite-state acceptor is represented as a transducer
with each transition's input and output label equal. Finite-state acceptors are
used to represent sets of strings (specifically, regular or rational sets);
finite-state transducers are used to represent binary relations between pairs
of strings (specifically, rational transductions). The weights can be used to
represent the cost of taking a particular transition.

This library was developed by contributors from Google Research and NYU's
Courant Institute. It is intended to be comprehensive, flexible, efficient and
scale well to large problems. it has been extensively tested. It is an open
source project distributed under the Apache license.