Revert "Fix String.deletingPathExtension Inconsistency"

This reverts commit c171fed.

Author: dduan

Foundation/NSPathUtilities.swift

@@ -68,8 +68,6 @@ internal extension String {
             } else if char == "." {
                 if lastCompStartPos == prevPos {
                     return nil
-                } else if case let prevPrevPos = index(before: prevPos), prevPos == index(before: endIndex) && prevPrevPos == lastCompStartPos && self[prevPrevPos] == "." {
-                    return nil
                 } else {
                     return curPos
                 }
@@ -264,7 +262,7 @@ public extension NSString {
         if fixedSelf.length <= 1 {
             return fixedSelf
         }
-        if let extensionPos = fixedSelf._startOfPathExtension {
+        if let extensionPos = (fixedSelf._startOfPathExtension) {
             return String(fixedSelf.prefix(upTo: fixedSelf.index(before: extensionPos)))
         } else {
             return fixedSelf

TestFoundation/TestNSString.swift

@@ -1078,7 +1078,6 @@ class TestNSString : XCTestCase {
             NSString(string: "scratch..tiff") : "scratch.",
             NSString(string: ".tiff") : ".tiff",
             NSString(string: "/") : "/",
-            NSString(string: "..") : "..",
         ]
         for (fileName, expectedResult) in values {
             let result = fileName.deletingPathExtension