Revert "[Type checker] Recurse into statements when cleaning type variables, harder."

This reverts commit 01913be.

Author: DougGregor

lib/Sema/ConstraintSystem.h

@@ -2411,6 +2411,12 @@ class ExprCleaner {
         TS->Patterns.insert({ P, P->getType() });
         return { true, P };
       }
+
+      // Don't walk into statements.  This handles the BraceStmt in
+      // non-single-expr closures, so we don't walk into their body.
+      std::pair<bool, Stmt *> walkToStmtPre(Stmt *S) override {
+        return { false, S };
+      }
     };
 
     E->walk(ExprCleanserImpl(this));

validation-test/compiler_crashers_fixed/28474-unreachable-executed-at-swift-lib-ast-type-cpp-1325.swift renamed to validation-test/compiler_crashers/28474-unreachable-executed-at-swift-lib-ast-type-cpp-1325.swift

@@ -5,5 +5,5 @@
 // See http://swift.org/LICENSE.txt for license information
 // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not %target-swift-frontend %s -emit-ir
+// RUN: not --crash %target-swift-frontend %s -emit-ir
 b<n([print{$0