zephyr: remove superfluous DEPLOY_DIR_IMAGE

Explicitly setting `DEPLOY_DIR_IMAGE` is not needed, since we have
`TEMPLATECONF`.
Setting `TEMPLATECONF` on the `source` step makes both `bitbake` and
`runqemu` steps share the same `DISTRO` setting, which sets
`DEPLOY_DIR_IMAGE` properly. Remove it from readme and conf-notes shown
after sourcing the env.

Signed-off-by: Wojciech Zmuda <wojciech.zmuda@huawei.com>

README.md

@@ -118,7 +118,7 @@ Example:
 
 You can test the image built for the qemu-x86 target by issuing:
 
-    $ DEPLOY_DIR_IMAGE=tmp-newlib/deploy/images/qemu-x86 runqemu qemu-x86
+    $ runqemu qemu-x86
 
 After successful bootup, you should see following:
 

flavours/zephyr/conf-notes.txt

@@ -14,5 +14,5 @@ or via command line, e.g.:
 
 You can also run generated qemu images with a command:
 
-    $ DEPLOY_DIR_IMAGE=tmp-newlib/deploy/images/qemu-x86 runqemu qemux86
+    $ runqemu qemux86