Revert "[Type checker] Introduce directional path consistency algorithm"

[shahmishal]

Reverts #4485

Due to test failure on Linux:

******************** TEST 'Swift(linux-x86_64) :: Sema/complex_expressions.swift' FAILED ********************
Script:
--
/home/buildnode/disk2/workspace/oss-swift-incremental-RA-linux-ubuntu-14_04/buildbot_incremental/swift-linux-x86_64/bin/swift -frontend -target x86_64-unknown-linux-gnu  -parse -verify -disable-objc-attr-requires-foundation-module /home/buildnode/disk2/workspace/oss-swift-incremental-RA-linux-ubuntu-14_04/swift/test/Sema/complex_expressions.swift
--
Exit Code: 1

Command Output (stderr):
--
/home/buildnode/disk2/workspace/oss-swift-incremental-RA-linux-ubuntu-14_04/swift/test/Sema/complex_expressions.swift:39:8: error: unexpected error produced: no such module 'Foundation'
import Foundation
       ^
<unknown>:0: error: fatal error encountered while in -verify mode

--