Revert "🔨 Rename BTT SKR V2.0 PIO envs (#27301)"

[thisiskeithb]

Description

This reverts commit 2f3af43 / #27301

"🔨 Rename BTT SKR V2.0 PIO envs (#27301)" does not accurately reflect what was actually done to my PR and we also specifically went from BIGTREE => BTT for board names in the past, so those unrelated changes seem backwards.

Even if we were to move everything back to "BIGTREE", it should be their actual name which is "BIGTREETECH".

Related Issues

• 🚸 Clarify BTT SKR V2.0 PIO environments #27301

[thinkyhead]

Most of the tests/ files, which are named exactly the same as the environment to which they pertain — all except one — are prefixed with "BIGTREE_" rather than "BTT_" so I renamed the odd one out (the env and the test). The rest of the PR should be exactly as it was originally crafted. Is there any part of the original PR that should be preserved?

[thinkyhead]

Even if we were to move everything back to "BIGTREE", it should be their actual name which is "BIGTREETECH".

A good point, which only stems due to the initiative of the original PR. Consistency is good, but there is a pretty even mixture of BTT/BIGTREE/BigTree/BIGTREETECH/BigTreeTech in naming of envs, boards, and variants. If full consistency is a goal, do we really want to change everything to either "BTT" or "BIGTREE" or "BIGTREETECH" across all references, folders, and filenames at some point? Considering this would involve changing several MOTHERBOARD names it seems like a good idea to hold off on this initiative until it can be done thoroughly. If the job had just been as small as the previous PR then it would be fine to merge it anytime, but as I've just tried to go through everything and move consistently to "BTT_" it's clear that doing a proper thoroughgoing job would be too disruptive at this moment. But we should slap it together soon after 2.1.3.