Remove `value` getter method from `Constant`

[Abhinav-Khot]

Description

The Constant class has a getter method value which just returns data. This PR removes this getter method since it is redundant.

Related Issue

• [ ] Closes #
• [ ] Related to #

Checklist

• [x] Checked that the pre-commit linting/style checks pass
• [ ] Included tests that prove the fix is effective or that the new feature works
• [ ] Added necessary documentation (docstrings and/or example notebooks)
• [ ] If you are a pro: each commit corresponds to a relevant logical change

Type of change

• [ ] New feature / enhancement
• [ ] Bug fix
• [ ] Documentation
• [x] Maintenance
• [ ] Other (please specify):

---

📚 Documentation preview 📚: https://pytensor--1317.org.readthedocs.build/en/1317/