[Discardable Shared Memory] Remove Windows (un)pinning support.
[Discardable Shared Memory] Remove Windows (un)pinning support.

Removing MEM_RESET and MEM_RESET_UNDO from Unlock and Lock
functions.  The overhead is a bit too high for some scenarios.
See ticket 595930 for details and plans for potential future
implementations.

BUG=180334,595930

Review URL: https://codereview.chromium.org/1832183002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#383514}

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