doc: Remove BSP layers

The layers have been removed from the project.

README.md

@@ -46,13 +46,11 @@ scripts/bbwrapper.sh at91sam gardena-image-foss-bnw linux-yocto-tiny
 * ```/``` Top level project.
  * ```/yocto/bitbake``` – the Bitbake build tool
  * ```/yocto/openembedded-core``` – OpenEmbedded core layer
- * ```/yocto/meta-mediatek``` – the MediaTek Board Support Package (BSP), used only for Art. No. 19005
  * ```/yocto/meta-distribution``` – our own distribution (specifies packages to install)
  * ```/yocto/meta-gardena``` – our own code (testing, WiFi provisioning, etc.)
  * ```/yocto/meta-openembedded``` – Collection of layers for the OE-core universe
  * ```/yocto/meta-readonly-rootfs-overlay``` – Writable rootfs overlay on top of a read-only rootfs
  * ```/yocto/meta-swupdate``` – Update mechanism software
- * ```/yocto/meta-atmel``` – our Atmel Board Support Package (BSP), used only for Art. No. 19000
 
 # Getting access