The instanceof cache was initially introduced to speed up

  x instanceof y

where y is always the same constructor and x is always an object with
the same map. With the introduction of ES2015's @@hasInstance and the
Function.prototype[Symbol.hasInstance] handler (which calls into
OrdinaryHasInstance), this already became quite useless. It doesn't seem
to provide any real value (not sure it ever did for real), but it's
getting in the way of some useful refactorings (i.e. sharing logic
between OrdinaryHasInstance and Object.prototype.isPrototypeOf for
example).

So this CL completely removes the leftover bits of the instanceof cache,
including the GC and SetPrototype logic.

BUG=v8:6479,v8:6474
R=jgruber@chromium.org
TBR=ulan@chromium.org

Review-Url: https://codereview.chromium.org/2932263002
Cr-Commit-Position: refs/heads/master@{#45835}