Bug 1870047, Bug 1870895 - Fix for 1-click set to default on MSIX builds causing the default browser to become Edge r=nalexander

This is a revision to remove the functionality that was added over 3 or 4 previous revisions to ultimately use Powershell to set the default browser in MSIX builds. On Windows with a new feature enabled by Microsoft, this results in the HTTP and HTTPS handler being reset to Edge, which is a terrible experience.
Since there's no solve, this is rolling that all back. Done as one set of changes here because it's all deleted code except for one line, a rollback isn't clean, and it would change the Javascript side to be non-async again, which isn't necessary.

This will effectively be reopening Bug 1818418 - Allow to use Windows UserChoice default mechanisms for MSIX packages. All of the bugs created in between were side effects of that change / fix.
I will not reopen that bug because we don't plan to fix it. Microsoft is rolling out new changes that explicitly disallow that mechanism. When it hits 100%, it won't work on any build type (MSIX or not).

Differential Revision: https://phabricator.services.mozilla.com/D197747

Author: mhughes-mozilla

browser/components/shell/WindowsUserChoice.cpp

@@ -284,21 +284,6 @@ UniquePtr<wchar_t[]> GetAssociationKeyPath(const wchar_t* aExt) {
   return keyPath;
 }
 
-nsresult AppendAssociationKeyPath(const wchar_t* aExt, nsString& output) {
-  if (aExt[0] == L'.') {
-    output.AppendLiteral(
-        u"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Explorer\\FileExts\\");
-  } else {
-    output.AppendLiteral(
-        u"SOFTWARE\\Microsoft\\Windows\\Shell\\Associations\\UrlAssociations"
-        u"\\");
-  }
-
-  output.Append(aExt);
-
-  return NS_OK;
-}
-
 UniquePtr<wchar_t[]> GenerateUserChoiceHash(const wchar_t* aExt,
                                             const wchar_t* aUserSid,
                                             const wchar_t* aProgId,

browser/components/shell/WindowsUserChoice.h

@@ -61,14 +61,6 @@ CheckUserChoiceHashResult CheckUserChoiceHash(const wchar_t* aExt,
  */
 mozilla::UniquePtr<wchar_t[]> GetAssociationKeyPath(const wchar_t* aExt);
 
-/*
- * Appends the registry path for the given association, file extension or
- * protocol to the parameter string.
- *
- * @return The path, or nullptr on failure.
- */
-nsresult AppendAssociationKeyPath(const wchar_t* aExt, nsString& output);
-
 /*
  * Get the current user's SID
  *