chore!: Remove web worker execution service and environment

[Mrtenz]

This is a redo of #3357, which was reverted in #3359 to avoid two breaking changes in a row. Now that #3322 is merged, we can do this again.

The original PR description can be found below.

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This removes the web worker execution service and execution environment, as they were unused. We can revert this PR in the future to add them again, if needed.

Breaking changes

@metamask/snaps-controllers

• Remove web worker execution service.

@metamask/snaps-execution-environments

• Remove web worker pool execution environment.
• Remove web worker executor execution environment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.04%. Comparing base (1d36a99) to head (9861942).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3371    +/-   ##
========================================
  Coverage   98.03%   98.04%            
========================================
  Files         402      398     -4     
  Lines       11107    10951   -156     
  Branches     1754     1725    -29     
========================================
- Hits        10889    10737   -152     
+ Misses        218      214     -4     

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