SERVER-13634 Get rid of all external callers of DiskLoc::rec()

DiskLoc::obj() and DiskLoc::btree() are the only remianing callers, other
than disabled tests.
SERVER-13555 Disable indexStats command

It is in the same boat as storageDetails. They will both be rewritten once
the correct abstraction layer is in place.
SERVER-13629 Remove old btree code and DiskLoc::btree/btreemod