Remove HAVE_ISDEBUGGERPRESENT.
Remove HAVE_ISDEBUGGERPRESENT.

It's equivalent to OS(WIN), and used only in Assertions.cpp. This CL removes it
for simplicity.
This CL has no behaivor changes.

BUG=

Review URL: https://codereview.chromium.org/1417093004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#357315}

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