Update properties template and documentation

Remove now unused python plugins key and add the new manifest key to the
documentation.

RE #28822

Framework/Properties/Mantid.properties.template

@@ -38,9 +38,6 @@ pvplugins.directory = @PV_PLUGINS_DIR@
 # Where to find Mantid Qt plugin libraries
 mantidqt.plugins.directory = @QT_PLUGINS_DIR@
 
-# Where to find python plugins
-python.plugins.directories = @PYTHONPLUGIN_DIRS@
-
 # Where to find the python plugin manifest file
 python.plugins.manifest = @PYTHONPLUGIN_MANIFEST@
 

Framework/PythonInterface/test/python/mantid/kernel/ConfigServiceTest.py

@@ -162,8 +162,7 @@ class ConfigServiceTest(unittest.TestCase):
                            'logging.channels.consoleChannel.class', 'logging.channels.consoleChannel.formatter', 'logging.formatters.f1.class', 'logging.formatters.f1.pattern', 'logging.formatters.f1.times', 'logging.loggers.root.channel.channel1', 'logging.loggers.root.channel.class',
                            'MantidOptions.ReusePlotInstances',
                            'mantidqt.python_interfaces', 'mantidqt.python_interfaces_directory',
-                           'paraview.ignore', 'paraview.path', 'paraview.pythonpaths', 'pvplugins.directory',
-                           'python.plugins.directories', "python.plugins.manifest"
+                           'paraview.ignore', 'paraview.path', 'paraview.pythonpaths', 'pvplugins.directory'
                            ]
 
         # create the list of things

docs/source/concepts/PropertiesFile.rst

@@ -112,7 +112,11 @@ Directory Properties
 |                                      | that Mantid requires to function correctly.       |                                     |
 |                                      | **WARNING:** Do not alter the default value.      |                                     |
 +--------------------------------------+---------------------------------------------------+-------------------------------------+
-
+| ``python.plugins.manifest``          | A path to the location of the manifest file       | N/A                                 |
+|                                      | containing paths to each of the python algorithm  |                                     |
+|                                      | files.                                            |                                     |
+|                                      | **WARNING:** Do not alter the default value.      |                                     |
++--------------------------------------+---------------------------------------------------+-------------------------------------+
 
 
 Logging Properties