winVersion: Deprecate Windows 7/8 constants (#15669)
Closes #15647
Summary of the issue:
Deprecate Windows 7/8 constants and change release name fetcher process.
Description of user facing changes
None
Description of development approach
Edit winVersion module:
Deprecate winVersion.WIN7/WIN7_SP1/WIN8 constants, replaced with getattr deprecation method.
Remove 6.1/6.2 checks from release name fetcher - only deal with Windows 8.1 and later.
For deprecated constants, provide release name field in getattr function.
