Deprecate inputDeviceInfo.getCapabilities() for better privacy

[jan-ivar]

From https://github.com/w3c/mediacapture-main/issues/669#issuecomment-605114117:

@henbos Specifically on removing required constraints, note that Chrome today implements info.getCapabilities() which gives the site capability information about all devices after gUM.

That API exists to allow a site to enforce its constraints while building a picker, or choosing another device outright. Most sites enforce some constraints.

That API is also a trove of fingerprinting information.

Luckily, "user-chooses" provides feature-parity with this, without the massive information leak:

await getUserMedia({video: constraints, semantics: "user-chooses"});

So merging https://github.com/w3c/mediacapture-main/pull/667 would let us retire info.getCapabilities() provided we leave constraints alone. 🎉

So far, it looks like only Chrome/Edge implement it (WPT)