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This was unused since at least 2016 (see crbug.com/657093). Remove the code to
support this both in LegacyLinker and ModernLinker. In the process, further
unify the two linkers, and refactor state tracking.

Bug: 979638

Change-Id: I4fad98228a841e1959a93f8ef5dbe5d29dfe7f30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715485Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Egor Pasko <pasko@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683155}