Revert "Documentation: admin-guide: add earlycon documentation for RISC-V"

This reverts commit 7f70ae564b807f81263326d641514c6dca88e5ef.

Christoph H. notes that the information is redundant, and Paul W. agrees
with reverting.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed