Revert "Start using xcode static paths for devicelab tests."

This reverts commit ba5856936ef4000296278399df02b0f06aa3a2d4.

Reason for revert: devicelab host tests need to use a separate path to install xcode.

Original change's description:
> Start using xcode static paths for devicelab tests.
>
> This is to avoid spending 10+ mins downloading and installing xcode on
> tasks that run for <5 mins. This also prevents the exit code -9 when
> installing/removing xcode.
>
> Change-Id: Ifb40345421f86498d4d05e1c8c665d7743c70802
> Bug: https://github.com/flutter/flutter/issues/68322
> Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/10620
> Reviewed-by: Casey Hillers <chillers@google.com>
> Commit-Queue: Godofredo Contreras <godofredoc@google.com>

TBR=godofredoc@google.com,chillers@google.com,flutter-scoped@luci-project-accounts.iam.gserviceaccount.com,mohsinally@google.com

Change-Id: Id77253d06fd11c71a079c985694ea28caf257aa4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: https://github.com/flutter/flutter/issues/68322
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/10640
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Commit-Queue: Godofredo Contreras <godofredoc@google.com>