Hardcode plugin id for UsbPrinter and XmlMaterialProfile

Previous solution was more defensive but also introduced dependencies
and extra files for minor benefit

CURA-6255

plugins/USBPrinting/USBPrinterOutputDevice.py

@@ -88,9 +88,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
         self._firmware_name_requested = False
         self._firmware_updater = AvrFirmwareUpdater(self)
 
-        from .USBPrinterOutputDeviceManager import USBPrinterOutputDeviceManager
-        plugin_id = USBPrinterOutputDeviceManager.getInstance().getPluginId()
-        plugin_path = PluginRegistry.getInstance().getPluginPath(plugin_id)
+        plugin_path = PluginRegistry.getInstance().getPluginPath("USBPrinting")
         self._monitor_view_qml_path = os.path.join(plugin_path, "MonitorItem.qml")
 
         CuraApplication.getInstance().getOnExitCallbackManager().addCallback(self._checkActivePrintingUponAppExit)

plugins/XmlMaterialProfile/XmlMaterialProfile.py

@@ -20,7 +20,6 @@ from UM.ConfigurationErrorMessage import ConfigurationErrorMessage
 from cura.CuraApplication import CuraApplication
 from cura.Machines.ContainerTree import ContainerTree
 from cura.Machines.VariantType import VariantType
-from plugins.XmlMaterialProfile import PluginInfo
 
 try:
     from .XmlMaterialValidator import XmlMaterialValidator
@@ -1070,8 +1069,7 @@ class XmlMaterialProfile(InstanceContainer):
     #   This loads the mapping from a file.
     @classmethod
     def getProductIdMap(cls) -> Dict[str, List[str]]:
-        plugin_id = PluginInfo.getInstance().getPluginId()
-        plugin_path = PluginRegistry.getInstance().getPluginPath(plugin_id)
+        plugin_path = PluginRegistry.getInstance().getPluginPath("XmlMaterialProfile")
         product_to_id_file = os.path.join(plugin_path, "product_to_id.json")
         with open(product_to_id_file, encoding = "utf-8") as f:
             product_to_id_map = json.load(f)

plugins/XmlMaterialProfile/__init__.py

@@ -1,6 +1,6 @@
 # Copyright (c) 2017 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
-from plugins.XmlMaterialProfile.PluginInfo import PluginInfo
+
 from . import XmlMaterialProfile
 from . import XmlMaterialUpgrader
 
@@ -46,5 +46,4 @@ def register(app):
 
     return {"version_upgrade": upgrader,
             "settings_container": XmlMaterialProfile.XmlMaterialProfile("default_xml_material_profile"),
-            "plugin_info": PluginInfo()
             }