Remove GradientArborescenceEmitter bounds

[btjanaka]

Description

Solution space bounds remain an open problem for DQD algorithms, and it is unclear that our implementation will create the correct behavior. Thus, we are removing the bounds handling for the time being.

TODO

Questions

Status

• [x] I have read the guidelines in CONTRIBUTING.md
• [x] I have formatted my code using yapf
• [x] I have tested my code by running pytest
• [x] I have linted my code with pylint
• [x] I have added a one-line description of my change to the changelog in HISTORY.md
• [x] This PR is ready to go