Drop MSP_MISC frame

[DzikuVx]

All clients should switch to MSP2_INAV_MISC and MSP2_SET_INAV_MISC

[sensei-hacker]

These commands are being marked as deprecated in #11315 first, to give third-party developers notice before removal.

[sensei-hacker]

Conflict resolution + docs gap completed:

• Merged maintenance-10.x into this branch (merge commit) to resolve the 2024-era staleness; conflicts resolved locally, preserving this PR's single-command drop and any newer commands that were adjacent in fc_msp.c/msp_protocol.h.
• Completed the missing docs: removed the dropped command's entry from docs/development/msp/msp_messages.json (version bumped 2.1.0 → 3.0.0, breaking schema change), removed the corresponding README.md section/TOC, and cleaned cross-references.
• Verified the drop is complete in the firmware handler (fc_msp.c), protocol header (msp_protocol.h), and docs.

CI is running; mergeable against maintenance-10.x.

[github-actions]

RAM / Flash usage vs. base branch — commit 853be53

No size baseline is available yet for this PR's base commit (no per-commit baseline has been published for it). This comment will show deltas once one exists — rebasing the PR refreshes its base commit.

Target	Flash Δ	RAM Δ
MATEKF405	700359 B (no baseline)	149532 B (no baseline)
MATEKF722	465075 B (no baseline)	125276 B (no baseline)
MATEKF765	732535 B (no baseline)	165468 B (no baseline)
MATEKH743	770615 B (no baseline)	167904 B (no baseline)

See RAM/flash optimization guide for techniques to reduce usage.

[github-actions]

Test firmware build ready — commit 853be53

Download firmware for PR #9921

247 targets built. Find your board's .hex file by name on that page (e.g. MATEKF405SE.hex). Files are individually downloadable — no GitHub login required.

Development build for testing only. Use Full Chip Erase when flashing.