remove unused IMU from demos

The demo launch files started IMU nodes that were
unused, produced warnings, and created problematic tf trees.
With this commit, they no longer start these nodes.
Quick tests of some of the demos indicate that they
work as well as they did before. However, I did not test
hello_world.launch.

stretch_demos/launch/clean_surface.launch

@@ -22,14 +22,6 @@
   </node>
   <!-- -->
 
-  <!-- IMU FILTER -->
-  <include file="$(find stretch_core)/launch/imu_filter.launch" />
-  <!-- -->
-
-  <!-- ROBOT LOCALIZATION FILTER -->
-  <include file="$(find stretch_core)/launch/stretch_ekf.launch" />
-  <!-- -->
-
   <!-- LASER RANGE FINDER -->
   <include file="$(find stretch_core)/launch/rplidar.launch" />
   <!-- -->

stretch_demos/launch/grasp_object.launch

@@ -22,14 +22,6 @@
   </node>
   <!-- -->
 
-  <!-- IMU FILTER -->
-  <include file="$(find stretch_core)/launch/imu_filter.launch" />
-  <!-- -->
-
-  <!-- ROBOT LOCALIZATION FILTER -->
-  <include file="$(find stretch_core)/launch/stretch_ekf.launch" />
-  <!-- -->
-
   <!-- LASER RANGE FINDER -->
   <include file="$(find stretch_core)/launch/rplidar.launch" />
   <!-- -->

stretch_demos/launch/handover_object.launch

@@ -21,14 +21,6 @@
   </node>
   <!-- -->
 
-  <!-- IMU FILTER -->
-  <include file="$(find stretch_core)/launch/imu_filter.launch" />
-  <!-- -->
-
-  <!-- ROBOT LOCALIZATION FILTER -->
-  <include file="$(find stretch_core)/launch/stretch_ekf.launch" />
-  <!-- -->
-
   <!-- LASER RANGE FINDER -->
   <include file="$(find stretch_core)/launch/rplidar.launch" />
   <!-- -->

stretch_demos/launch/hello_world.launch

@@ -25,14 +25,6 @@
   </node>
   <!-- -->
 
-  <!-- IMU FILTER -->
-  <include file="$(find stretch_core)/launch/imu_filter.launch" />
-  <!-- -->
-
-  <!-- ROBOT LOCALIZATION FILTER -->
-  <include file="$(find stretch_core)/launch/stretch_ekf.launch" />
-  <!-- -->
-
   <!-- LASER RANGE FINDER -->
   <include file="$(find stretch_core)/launch/rplidar.launch" />
   <!-- -->

stretch_demos/launch/open_drawer.launch

@@ -22,14 +22,6 @@
   </node>
   <!-- -->
 
-  <!-- IMU FILTER -->
-  <include file="$(find stretch_core)/launch/imu_filter.launch" />
-  <!-- -->
-
-  <!-- ROBOT LOCALIZATION FILTER -->
-  <include file="$(find stretch_core)/launch/stretch_ekf.launch" />
-  <!-- -->
-
   <!-- LASER RANGE FINDER -->
   <include file="$(find stretch_core)/launch/rplidar.launch" />
   <!-- -->