Bug 1804113: stop implicitly pinning to taskbar r=bytesized

Two parts here:
1) Remove the code that does implicit pinning entirely (this will disable it on Windows 7 as well, which I think is probably the right thing to do at this point).
2) Fix the installer to set a proper default for AddTaskbarSC

Differential Revision: https://phabricator.services.mozilla.com/D164096

browser/installer/windows/nsis/installer.nsi

@@ -415,6 +415,11 @@ Section "-Application" APP_IDX
     StrCpy $AddDesktopSC "1"
   ${EndIf}
 
+  ; Default for adding a Taskbar pin (1 = pin, 0 = don't pin)
+  ${If} $AddTaskbarSC == ""
+    StrCpy $AddTaskbarSC "1"
+  ${EndIf}
+
   ${LogHeader} "Adding Registry Entries"
   SetShellVarContext current  ; Set SHCTX to HKCU
   ${RegCleanMain} "Software\Mozilla"

browser/installer/windows/nsis/shared.nsh

@@ -1284,24 +1284,7 @@ ${RemoveDefaultBrowserAgentShortcut}
         "Software\Mozilla\${AppName}\Installer\$AppUserModelID" \
         "WasPinnedToTaskbar" 1
       ${If} ${AtLeastWin7}
-        ; If we didn't run the stub installer, AddTaskbarSC will be empty.
-        ; We determine whether to pin based on whether we're the default
-        ; browser, or if we're on win8 or later, we always pin.
-        ${If} "${SHOULD_PIN}" == ""
-          ; No need to check the default on Win8 and later
-          ${If} ${AtMostWin2008R2}
-            ; Check if the Firefox is the http handler for this user
-            SetShellVarContext current ; Set SHCTX to the current user
-            ${IsHandlerForInstallDir} "http" $R9
-            ${If} $TmpVal == "HKLM"
-              SetShellVarContext all ; Set SHCTX to all users
-            ${EndIf}
-          ${EndIf}
-          ${If} "$R9" == "true"
-          ${OrIf} ${AtLeastWin8}
-            ${PinToTaskBar}
-          ${EndIf}
-        ${ElseIf} "${SHOULD_PIN}" == "1"
+        ${If} "${SHOULD_PIN}" == "1"
           ${PinToTaskBar}
         ${EndIf}
       ${EndIf}