Delete the NPMI plugin. (#6259)

The NPMI plugin was an intern project but was never completed. It's time
to delete it.

Author: bmd3k

tensorboard/BUILD

@@ -316,7 +316,6 @@ py_library(
         "//tensorboard/plugins/image:images_plugin",
         "//tensorboard/plugins/mesh:mesh_plugin",
         "//tensorboard/plugins/metrics:metrics_plugin",
-        "//tensorboard/plugins/npmi:npmi_plugin",
         "//tensorboard/plugins/pr_curve:pr_curves_plugin",
         "//tensorboard/plugins/profile_redirect:profile_redirect_plugin",
         "//tensorboard/plugins/scalar:scalars_plugin",

tensorboard/default.py

@@ -29,7 +29,6 @@
 
 import pkg_resources
 
-from tensorboard.backend import experimental_plugin
 from tensorboard.plugins.audio import audio_plugin
 from tensorboard.plugins.core import core_plugin
 from tensorboard.plugins.custom_scalar import custom_scalars_plugin
@@ -45,20 +44,11 @@
 from tensorboard.plugins.scalar import scalars_plugin
 from tensorboard.plugins.text import text_plugin
 from tensorboard.plugins.mesh import mesh_plugin
-from tensorboard.plugins.npmi import npmi_plugin
 
 
 logger = logging.getLogger(__name__)
 
 
-class ExperimentalNpmiPlugin(
-    npmi_plugin.NpmiPlugin, experimental_plugin.ExperimentalPlugin
-):
-    """Angular nPMI Plugin marked as experimental."""
-
-    pass
-
-
 # Ordering matters. The order in which these lines appear determines the
 # ordering of tabs in TensorBoard's GUI.
 _PLUGINS = [
@@ -77,7 +67,6 @@ class ExperimentalNpmiPlugin(
     profile_redirect_plugin.ProfileRedirectPluginLoader,
     hparams_plugin.HParamsPlugin,
     mesh_plugin.MeshPlugin,
-    ExperimentalNpmiPlugin,
 ]