Drop the retargeting of accNavigate in BrowserAccessibilityWin

AXPlatformNode already retargets based on the start variant, so we can drop
the GetTargetFromChildID call for GetPlatformNodeWin()->accNavigate.

BUG=703369

Review-Url: https://codereview.chromium.org/2851093002
Cr-Commit-Position: refs/heads/master@{#468412}
1 file changed