Reduce axiom usage

[GinoGiotto]

Edit a few proofs to reduce axiom usage, specifically:

• Edit cgsex4g -> Avoid ax-11
• Edit ss2abdv -> Avoid ax-8, ax-10, ax-11, ax-12
• Edit ss2abi -> Avoid ax-8, ax-10, ax-11, ax-12
• Edit eq0 -> Avoid ax-11, ax-12
• Edit neq0 -> Avoid ax-11, ax-12
• Edit n0 -> Avoid ax-11, ax-12
• Edit rspn0 -> Avoid -> ax-10, ax-12 (ax-11 is automatically removed by previous edits)
• Edit abf -> Avoid ax-8, ax-10, ax-11, ax-12
• Edit csb0 -> Avoid ax-12 (ax-10, ax-11 are automatically removed by previous edits)
• Edit disj -> Avoid ax-10, ax-11, ax-12
• Edit reldisj -> Avoid ax-12 (ax-10, ax-11 are automatically removed by previous edits)
• Replace elab2 with elab2gw in elint proof -> Avoid ax-10, ax-11, ax-12 (this is a simple replacement, so credits and OLD proof are not provided here).

All added dv conditions are with dummy variables.

Result: Drop ax-12 from 345 theorems. Drop ax-11 from 439 theorems. Drop ax-10 from 224 theorems. Drop ax-8 From 3 theorems.

Axiom usage here: https://github.com/metamath/set.mm/commit/271a059d8184be3cdcbd32de685a7e0ce4b61b5c