CB-13382 dealloc the webViewEngine

[surajpindoria]

Platforms affected

iOS

What does this PR do?

Adds an additional clean up step to dealloc

What testing has been done on this change?

Checklist

• Reported an issue in the JIRA database
• Commit message follows the format: "CB-3232: (android) Fix bug with resolving file paths", where CB-xxxx is the JIRA ID & "android" is the platform affected.
• Added automated test coverage as appropriate for this change.

[codecov-io]

Codecov Report

Merging #359 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #359   +/-   ##
=======================================
  Coverage   63.99%   63.99%           
=======================================
  Files          14       14           
  Lines        1697     1697           
  Branches      286      286           
=======================================
  Hits         1086     1086           
  Misses        611      611

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