gnu: Remove Tailon services and documentation.

The tailon package was removed in 63023deaf96bd0d90aba262b194bf1445ec5a0b6,
but the associated service and documentation weren’t, leading to `guix pull`
breaking.

Fixes guix/guix#2689.

* doc/guix.texi: Remove Tailon documentation.
* gnu/services/web.scm (tailon-service-type): Delete variable.
(tailon-configuration-file): Delete variable.
(tailon-configuration-file?): Delete variable.
(tailon-configuration-file-files): Delete variable.
(tailon-configuration-file-bind): Delete variable.
(tailon-configuration-file-relative-root): Delete variable.
(tailon-configuration-file-allow-transfers?): Delete variable.
(tailon-configuration-file-follow-names?): Delete variable.
(tailon-configuration-file-tail-lines): Delete variable.
(tailon-configuration-file-allowed-commands): Delete variable.
(tailon-configuration-file-debug?): Delete variable.
(tailon-configuration-file-http-auth): Delete variable.
(tailon-configuration-file-users): Delete variable
(tailon-configuration): Delete variable.
(tailon-configuration?): Delete variable.
(tailon-configuration-config-file): Delete variable.
(tailon-configuration-package): Delete variable.
* gnu/tests/web.scm (%test-tailon): Delete variable.

Change-Id: I3b507df8233b0440baa6a2bce4604b5813cb3bb0

gnu: Remove python-pylzma.

* gnu/packages/python-xyz.scm (python-pylzma): Delete variable.

Fixes: guix/guix#1919
Change-Id: Icad9f8b8dfc23406271c5e3cd342e5553dbde491

gnu: Remove warsow-qfusion.

* gnu/packages/game-development.scm (warsow-qfusion): Delete variable.

Fixes: guix/guix#1911
Change-Id: Ibad0428d559556ed3fedc5ae99702222d0dafa98

gnu: Remove cawbird.

* gnu/packages/syndication.scm (cawbird): Delete variable.

Fixes: guix/guix#1907
Change-Id: Ifd4bb5e40113d574076b3458d4c24b130d1c4b2b

gnu: Remove farstream.

* gnu/packages/freedesktop.scm (farstream): Delete variable.

Fixes: guix/guix#1906
Change-Id: I067d553ac39f6370d8b0f321d682a7854d6ac9ac

gnu: Remove nomad.

* gnu/packages/guile-xyz.scm (nomad): Delete variable.

Fixes: guix/guix#1905
Change-Id: Ie0e814184072a6c3920e2de0310adeef8361e299

gnu: Remove python-rrdtool.

* gnu/packages/monitoring.scm (python-rrdtool): Delete variable.

Fixes: guix/guix#1896
Change-Id: I683bbaa5cb42ff363dd12771269a0a0c08f9a979

gnu: Remove graphite-web.

* gnu/packages/monitoring.scm (graphite-web): Delete variable.

Change-Id: I0e7b8506d8690c8efc083f82373b221729b23e96

gnu: Remove openni2.

* gnu/packages/gstreamer.scm (openni2): Delete variable.

Fixes: guix/guix#1891
Change-Id: If4c58002f41c0aef87c90113553abbc27e76d7cd

gnu: Remove clang-runtime-6.

* gnu/packages/llvm.scm (clang-runtime-6): Delete variable.
* gnu/packages/patches/clang-runtime-9-glibc-2.36-compat.patch.
gnu/packages/patches/clang-runtime-9-libsanitizer-mode-field.patch:
Delete files.
* gnu/local.mk (dist_patch_DATA): Unregister files.

Change-Id: I2957376d083783e77de85a9761be06d0209ca6c7

gnu: Remove clang-6.

* gnu/packages/llvm.scm (clang-6): Delete variable.
* gnu/packages/patches/clang-6.0-libc-search-path.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Unregister file.

Change-Id: Ife89d032bd5edbbc2613dbef71e5e8434d75c979

gnu: Remove libomp-6.

* gnu/packages/llvm.scm (libomp-6): Delete variable.

Change-Id: If0acf3036fcf8afec7467d864dce9b56dcb2c804

gnu: Remove libcxx-6.

* gnu/packages/llvm.scm (libcxx-6): Delete variable.

Change-Id: I94d7d2db5c98f0abea4c0142d9d996f9ece8b03b

gnu: Remove libcxxabi-6.

* gnu/packages/llvm.scm (libcxxabi-6): Delete variable.

Change-Id: I5bfad857a489d4dd513a15aaec52668a0eeb3d81

gnu: Remove libcxx+libcxxabi-6.

* gnu/packages/llvm.scm (libcxx+libcxxabi-6): Delete variable.

Change-Id: Ie1cdb96d1d2b303e8a7c30ee958315e8aa057810

gnu: Remove clang-toolchain-6.

* gnu/packages/llvm.scm (clang-toolchain-6): Delete variable.

Change-Id: I308e022ac72f9f66339af3356c3071955707f397

gnu: Remove fmt-6.

* gnu/packages/pretty-print.scm (fmt-6): Delete variable.

Change-Id: I17cb2e67878f13cbe9e8f40b671fa5010cd97974

gnu: Remove snappy-with-clang6.

* gnu/packages/compression.scm (snappy-with-clang6): Delete variable.

Change-Id: Ia3a3e534acf77ebf6edea3f2f9482c4e96ac1e38

gnu: Remove nanodbc-for-irods.

* gnu/packages/databases.scm (nanodbc-for-irods): Delete variable.

Change-Id: I7b6aecc3b21589e2a9b53974046c7a03e954c3fc

gnu: Remove boost-for-irods.

* gnu/packages/boost.scm (boost-for-irods): Delete variable.

Change-Id: I1bc02caa35a4eb8a49ce28348631e4fc69167579