swift234

Revert "[ObjC Interop] Map Swift @objc properties named isFoo to ObjC Cocoa conventions" (#3254)

It sounds good on paper, but in practice we ended up breaking Core Data
projects (because people name their boolean properties 'isFoo' rather
than the Objective-C 'foo'), forcing an Objective-C-side change when
a mixed-source project upgrades to Swift 3, and causing collisions when
there are properties named both 'foo' and 'isFoo'. If people care about
their Swift boolean properties strictly following the Objective-C Cocoa
naming conventions, they'll have to specify them manually.

(We do have a bug to make it easier to rename the getter of a stored
property exposed to Objective-C: rdar://problem/21261564.)

This reverts commit 6fe6266c999b036d8c7ab428c1c3c2fe8be1a42e.

rdar://problem/26847223