Fix load plugin dimension

This change removes a line that set the dimension to be None. In
that way, the dimensions of the measurement can be set through the
plugin configuration file.

Change-Id: I038ee56f58426a79c27f65427de6d58ca4d0952e

conf.d/load.yaml

@@ -5,3 +5,6 @@ init_config:
 instances:
     # Load check only supports one configured instance
     - name: load_stats
+      # (optional) Additional dimensions to dimensions each metric with
+      # dimensions:
+      #   dim1: value1

monasca_agent/collector/checks_d/load.py

@@ -49,8 +49,6 @@ class Load(checks.AgentCheck):
         # Split out the 3 load average values
         load = [res.replace(',', '.') for res in re.findall(r'([0-9]+[\.,]\d+)', uptime)]
 
-        dimensions = self._set_dimensions(None)
-
         #
         # Normalize the load averages by number of cores
         # so the metric is useful for alarming across