mac: Remove IsOSSnowLeopard().

BUG=579255
TBR=erikchen, thestig

Review URL: https://codereview.chromium.org/1849343003

Cr-Original-Commit-Position: refs/heads/master@{#384946}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 708618eab03e7fbac19035ac78c1c2a4c0e72495
1 file changed