Rename DCHECK_CURRENTLY_ON_WEB_THREAD to DCHECK_CURRENTLY_ON.
Rename DCHECK_CURRENTLY_ON_WEB_THREAD to DCHECK_CURRENTLY_ON.

Remove support macro DCHECK_CURRENTLY_ON_WEB_THREAD as it is no
longer used.

BUG=438202

Review URL: https://codereview.chromium.org/1707313002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#376723}

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