Remove FORCE_ENABLE_WKWEBVIEW as bots pass the command-line flag.
Remove FORCE_ENABLE_WKWEBVIEW as bots pass the command-line flag.

FORCE_ENABLE_WKWEBVIEW compilation define is no longer required as
all the bots pass the correct command-line flag.

BUG=450311

Review URL: https://codereview.chromium.org/1595483002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#369719}

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