🧹 [code health improvement] mtdsplit: tplink: Remove unused boot_ofs and boot_len fields

[ManupaKDU]

🎯 What: Removed unused boot_ofs and boot_len fields from struct fw_v1 and struct fw_v2 in mtdsplit_tplink.c.
💡 Why: These fields were marked as FIXME and never referenced in the codebase. Removing them cleans up dead code and improves readability.
✅ Verification: Replaced the removed 8 bytes with explicit padding (pad1[8] in fw_v2 and increasing pad from 360 to 368 in fw_v1) to guarantee the 508-byte total size and internal offsets of the __attribute__((packed)) structures remain completely unchanged. Compiled a mock script and ran the full CI test suite successfully to confirm ABI safety.
✨ Result: Cleaner firmware header structures without introducing any regressions or binary layout changes.

Signed-off-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

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PR created automatically by Jules for task 16964385517997740705 started by @manupawickramasinghe

[google-labs-jules]

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