Remove 'enable_service tempest' from sample/local.conf

tempest is already defined in stackrc as default.
Without this definition in local.conf,
tempest is installed successfully.

If it still needs "enable_service tempest" definition
on local.conf,
devstack itself has some problem.
In my environment, tempest installation works
without this definition on local.conf.

Change-Id: I25cda0142538d21bb9656b471e65ca5b018e8378

Author: sakaia

samples/local.conf

@@ -93,9 +93,3 @@ SWIFT_REPLICAS=1
 # moved by setting ``SWIFT_DATA_DIR``. The directory will be created
 # if it does not exist.
 SWIFT_DATA_DIR=$DEST/data
-
-# Tempest
-# -------
-
-# Install the tempest test suite
-enable_service tempest