Remove vishwath@google.com from core/java/android/security/OWNERS

This suggested change is automatically generated based on group
memberships and affiliations.
If this change is unnecessary or in error, vote CR -1 and the bot
will abandon it. Vote CR +1/2 to approve this change.

See the owner's recent activity for context:
https://googleplex-android-review.googlesource.com/q/vishwath@google.com

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Change-Id: Id065c2cb1b2d3be42fd360e6b06700a2fbcbe6bd