Revert "Store a z-index id per-layer (#4128)" (#4133)

This reverts commit 28a23372185c7a30c7790085a6a010c3cad6ad09, reversing
changes made to e992f84735a2ca166a7388d4eca69a6b4e6ee212.

[[PR Description]]

Release Notes:

- (Added|Fixed|Improved) ...
([#<public_issue_number_if_exists>](https://github.com/zed-industries/community/issues/<public_issue_number_if_exists>)).
d64207e009Conrad Irwin committed on 1/18/2024, 8:36:34 PM· committed by GitHubparents81baefb6c2da0d
7 files changedLine totals unavailable