Remove obsolete part of README

Getting tarball hash is not needed anymore, qubesbuilderv2 takes care of
git tag verification.

Author: marmarek

README.md

@@ -5,18 +5,4 @@ Building release candidate kernels
 ----------------------------------
 
 1. Write kernel version into `version` file, for example 6.0-rc7.
-2. Write hash of `linux-*.tar` file (the uncompressed source tarball) into `linux-*.tar.sha256` file.
-3. Comment out "normal" tarball section in `.qubesbuilder` and uncomment the one for rc kernel.
-
-
-As for getting the trustworthy tarball hash, it can be via signed git tag:
-
-```
-version=6.0-rc7
-git clone -n --depth=1 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git -b v$version linux-rc
-cd linux-rc
-git verify-tag v$version
-# should be signed by Linus, you can find key in kernel.org-1-key.asc
-git archive --prefix=linux-$version/ v$version | sha256sum
-```
-
+2. Comment out "normal" tarball section in `.qubesbuilder` and uncomment the one for rc kernel.