arm-bsp/corstone500: removal of support

corstone500 is End-of-life'd (EOL'ed).  Remove support for it from the
tree.

Signed-off-by: Jon Mason <jon.mason@arm.com>

kas/corstone500.yml

@@ -1,50 +0,0 @@
-header:
-  version: 11
-  includes:
-    - kas/fvp-eula.yml
-
-env:
-  DISPLAY: ""
-
-distro: poky-tiny
-
-defaults:
-  repos:
-    refspec: master
-
-repos:
-  meta-arm:
-    layers:
-      meta-arm:
-      meta-arm-bsp:
-      meta-arm-toolchain:
-
-  poky:
-    url: https://git.yoctoproject.org/git/poky
-    refspec: master
-    layers:
-      meta:
-      meta-poky:
-      meta-yocto-bsp:
-
-  meta-openembedded:
-    url: https://git.openembedded.org/meta-openembedded
-    refspec: master
-    layers:
-      meta-oe:
-      meta-python:
-
-local_conf_header:
-  base: |
-    CONF_VERSION = "2"
-    PACKAGE_CLASSES = "package_ipk"
-    BB_NUMBER_THREADS ?= "16"
-    PARALLEL_MAKE ?= "-j16"
-    PACKAGECONFIG:append:pn-perf = " coresight"
-  fvp-config: |
-    IMAGE_CLASSES:append = " ${@bb.utils.contains('BUILD_ARCH', 'x86_64', 'fvpboot', '', d)}"
-
-machine: corstone500
-
-target:
-  - core-image-minimal