Move "metered" persistence to WifiConfiguration.

For a long time we've had a nasty tangled dependency between Wi-Fi
and NPMS, since they both persisted different details for configured
networks.  As part of preparing for new carrier data plan APIs, move
the tracking of meteredness over to WifiConfiguration.

This also cleans up how meteredness is communicated through
NetworkAgents to rely completely on NET_CAPABILITY_NOT_METERED by
removing the metered flag on NetworkInfo, which has caused confusion
and staleness.

Migrates any existing user-configured metered networks over to
WifiConfiguration once the device finishes booting.

Remove support for NetworkQuotaInfo, since this information can no
longer be made available to apps.  Frustratingly, some apps are
using it, so keep the object around returning stub values, and shame
them in the logs.

Bug: 63391323
Test: builds, boots, Wi-Fi policy is upgraded
Exempt-From-Owner-Approval: Bug 63673347
Change-Id: I64f865ddeb65cfcd330f8d2a847368abdf960a07