AudioPluginFormat: Remove canScanOnBackgroundThread(), as it is not generally useful

modules/juce_audio_processors/format/juce_AudioPluginFormat.h

@@ -115,9 +115,6 @@ public:
     */
     virtual bool isTrivialToScan() const = 0;
 
-    /** Should return true if plugins in this format can be scanned on a background thread. */
-    virtual bool canScanOnBackgroundThread() const { return true; }
-
     /** Searches a suggested set of directories for any plugins in this format.
         The path might be ignored, e.g. by AUs, which are found by the OS rather
         than manually.

modules/juce_audio_processors/format_types/juce_VST3PluginFormat.h

@@ -61,13 +61,6 @@ public:
     bool canScanForPlugins() const override         { return true; }
     bool isTrivialToScan() const override           { return false; }
 
-    /** Although there doesn't seem to be any official documentation on the matter,
-        Native Instruments Kontakt VST3 crashes on macOS when its bundleEntry is called on a
-        background thread. To allow this plugin (and other ones with similar problems) to be
-        discovered, it's a good idea to scan VST3 plugins on the main thread.
-    */
-    bool canScanOnBackgroundThread() const override { return false; }
-
     void findAllTypesForFile (OwnedArray<PluginDescription>&, const String& fileOrIdentifier) override;
     bool fileMightContainThisPluginType (const String& fileOrIdentifier) override;
     String getNameOfPluginFromIdentifier (const String& fileOrIdentifier) override;

modules/juce_audio_processors/scanning/juce_PluginListComponent.cpp

@@ -393,8 +393,8 @@ public:
           propertiesToUse (properties),
           pathChooserWindow (TRANS("Select folders to scan..."), String(), MessageBoxIconType::NoIcon),
           progressWindow (title, text, MessageBoxIconType::NoIcon),
-          numThreads (format.canScanOnBackgroundThread() ? threads : 0),
-          allowAsync (format.canScanOnBackgroundThread() && allowPluginsWhichRequireAsynchronousInstantiation)
+          numThreads (threads),
+          allowAsync (allowPluginsWhichRequireAsynchronousInstantiation)
     {
         FileSearchPath path (formatToScan.getDefaultLocationsToSearch());