issue: Remove unused XLIO_BF

[pasis]

TODO Ticket number

Description

Remove the XLIO_BF parameter as a leftover.

BlueFlame support has been removed. Besides, XLIO_BF was unused and an rdma-core specific env parameter was checked instead.

What

Remove the XLIO_BF parameter.

Why ?

Unused parameter.

Change type

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update
• [x] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [x] Documentation content changes
• [ ] Tests
• [ ] Other

Check list

• [ ] Code follows the style de facto guidelines of this project
• [ ] Comments have been inserted in hard to understand places
• [ ] Documentation has been updated (if necessary)
• [ ] Test has been added (if possible)