gnu: Remove linux-libre 6.3.
This kernel series is no longer supported upstream.
* gnu/packages/linux.scm (linux-libre-6.3-version, linux-libre-6.3-gnu-revision,
deblob-scripts-6.3, linux-libre-6.3-pristine-source, linux-libre-6.3-source,
linux-libre-headers-6.3, linux-libre-6.3): Remove variables.
* gnu/packages/aux-files/linux-libre/6.3-arm.conf,
gnu/packages/aux-files/linux-libre/6.3-arm64.conf,
gnu/packages/aux-files/linux-libre/6.3-i686.conf,
gnu/packages/aux-files/linux-libre/6.3-x86_64.conf: Delete files.
* Makefile.am (AUX_FILES): Remove them.
* gnu/packages/patches/linux-libre-wireguard-postup-privkey.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Remove it.
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