README.md : Remove LSB related content that is deprecated

No longer support Linux Standard Base (LSB) since version 3.0
core-image-lsb-sdk recipes are removed
So remove the related content

https://www.yoctoproject.org/docs/3.0/ref-manual/ref-manual.html#migration-3.0-lsb-support-removed



Signed-off-by: sungwon.pino <sungwon.pino@gmail.com>