Remove dead code from install.sh and install.ps1

[dustinvannoy-db]

Pure cleanup of confirmed dead/unreachable/vestigial code in the two top-level installer scripts. No behavior change — every deletion was verified to have zero reachable call sites or reads.

Deleted

File	Symbol	Why it's dead
install.sh	deprecation_notice()	Zero call sites. The "skills are moving" announcement has already shipped and is being retired, so the call was not restored.
install.ps1	Show-DeprecationNotice	Zero call sites, same reason.
install.ps1	$VenvDir / $VenvPython block	Never read. The venv now lives in databricks-mcp-server/mcp_install.ps1, and Invoke-Uninstall edits JSON via ConvertFrom-Json/ConvertTo-Json rather than shelling out to a Python interpreter.
install.ps1	$line = " " in $drawCheckbox	Assigned, never read.
install.ps1	$i++ after Write-Err in the arg-parse default arm	Unreachable — Write-Err ends in exit 1.

The bash VENV_PYTHON is genuinely live (read at three call sites) and was deliberately left in place — only the PowerShell counterpart was dead.

Explicitly left untouched

• All MCP deprecation shims: Show-McpMovedNotice / mcp_moved_notice and the --mcp / -Mcp, --mcp-path / -McpPath, --mcp-only / -McpOnly, and DEVKIT_INSTALL_MCP arms — reachable, they warn and point at mcp_install.
• The --skills-only / -SkillsOnly arm despite its empty body — load-bearing, since removing it would make the flag fall through to the error/exit path.
• The $AgentBExcluded / AGENT_B_EXCLUDED empty-array knob and its no-op loops — a documented deliberate knob.
• The uninstall MCP-cleanup helpers (Test-McpJsonHasDatabricks, Remove-McpJsonKey, Remove-McpTomlBlock) and their mcpTargets/planMcp plumbing.
• $script:InstallSkills always-true const — cosmetic, out of scope.

Gates

• bash -n install.sh — passes.
• shellcheck install.sh — 49 findings before, 49 after, and the normalized finding set is byte-identical (diff clean). No new warnings.
• install.ps1 parse check — not run: no PowerShell binary is installed on the machine used for this change (pwsh, powershell, and the usual /usr/local/microsoft/powershell install paths are all absent). The PowerShell edits are localized deletions of whole function definitions, a variable-assignment block, and two single statements, but the parse gate is genuinely unverified and should be confirmed on a host with pwsh.
• Post-deletion re-grep: deprecation_notice, Show-DeprecationNotice, VenvPython, VenvDir, and $line = " " all have zero occurrences; all KEEP-list symbols are still present at their expected sites.

Co-authored-by: omnigent noreply@omnigent.ai

This pull request and its description were written by Isaac.