Revert "[build-tools] Pin the default agent-device version for remote sessions (#4142)"

[szdziedzic]

Why

Reverts #4142 ("[build-tools] Pin the default agent-device version for remote sessions").

How

git revert of commit f56c054. The default agent-device version for remote sessions goes back to latest when the package_version input is not set:

• DEFAULT_AGENT_DEVICE_VERSION is removed.
• packageVersion is string | undefined again in startAgentDeviceDaemonAsync, startAgentDeviceDaemonFromGitAsync, cloneAgentDeviceAsync, and createAgentDevicePackageSpec.
• The npm package spec falls back to agent-device@latest, and the git clone omits --branch when no version is given.

The CHANGELOG entry for #4142 stays in the 21.5.0 section because that change already shipped in @expo/build-tools@21.5.1. A new entry under ## main records the revert.

Test Plan

• yarn typecheck — passes.
• yarn lint — passes (0 errors).
• yarn fmt:check — passes.
• yarn lint-changelog — passes.
• cd packages/build-tools && yarn test — 104 of 105 suites pass. The one failure is steps/functions/__tests__/repack.test.ts, which fails the same way on the base commit d003bffa (spawn yarn ENOENT in the local sandbox) and is unrelated to this change.

🤖 Generated with Claude Code

[github-actions]

✅ Thank you for adding the changelog entry!

[codecov]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.43%. Comparing base (b27fe84) to head (48081d1).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/steps/functions/startAgentDeviceRemoteSession.ts	0.00%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4145   +/-   ##
=======================================
  Coverage   62.43%   62.43%           
=======================================
  Files        1009     1009           
  Lines       45735    45735           
  Branches     9621     9621           
=======================================
  Hits        28548    28548           
  Misses      15726    15726           
  Partials     1461     1461           

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