Remove sample{} from template examples

.. when creating a user chart or a user metric the template
   code included calls to sample{}

   seemed odd to warn it was a serious performance issue
   whilst at the same time using it in the template.

.. we should just deprecate sample{} altogether, will likely
   make that change before the release of v3.6

src/Charts/UserChart.cpp

@@ -1640,11 +1640,6 @@ EditUserSeriesDialog::EditUserSeriesDialog(Context *context, bool rangemode, Gen
             "        Data contains \"P\";\n"
             "    }\n"
             "\n"
-            "    sample {\n"
-            "        # as we iterate over activity data points\n"
-            "        count <- count + 1;\n"
-            "    }\n"
-            "\n"
             "    finalise {\n"
             "        # we just fetch samples at end\n"
             "        xx <- samples(SECS);\n"

src/Gui/Pages.cpp

@@ -1937,7 +1937,8 @@ CustomMetricsPage::addClicked()
     here.name = "My Average Power";
     here.type = 1;
     here.precision = 0;
-    here.description = "Average Power computed using Joules to account for variable recording.";
+    here.istime = false;
+    here.description = "Average Power";
     here.unitsMetric = "watts";
     here.unitsImperial = "watts";
     here.conversion = 1.00;
@@ -1947,17 +1948,12 @@ CustomMetricsPage::addClicked()
     relevant { Data contains \"P\"; }\n\
 \n\
     # initialise aggregating variables\n\
-    init { joules <- 0; seconds <- 0; }\n\
-\n\
-    # joules = power x time, for each sample\n\
-    sample { \n\
-        joules <- joules + (POWER * RECINTSECS);\n\
-        seconds <- seconds + RECINTSECS;\n\
-    }\n\
+    # does nothing, update as needed\n\
+    init { 0; }\n\
 \n\
     # calculate metric value at end\n\
-    value { joules / seconds; }\n\
-    count { seconds; }\n\
+    value { mean(samples(POWER)); }\n\
+    count { count(samples(POWER)); }\n\
 }";
 
     EditUserMetricDialog editor(this, context, here);