home: vim: do not use 'ftplugin' for 'null-ls'

Unfortunately, this registers the sources many times...

I fear that I will have to settle for a centralised configuration for
LSP-related options.

home/vim/after/ftplugin/python.vim

@@ -1,36 +0,0 @@
-" Create the `b:undo_ftplugin` variable if it doesn't exist
-call ftplugined#check_undo_ft()
-
-" Set-up LSP, linters, formatters
-lua << EOF
-local null_ls = require("null-ls")
-local utils = require("ambroisie.utils")
-
-null_ls.register({
-    null_ls.builtins.diagnostics.flake8.with({
-        -- Only used if available
-        condition = utils.is_executable_condition("flake8"),
-    }),
-    null_ls.builtins.diagnostics.mypy.with({
-        -- Only used if available
-        condition = utils.is_executable_condition("mypy"),
-    }),
-    null_ls.builtins.diagnostics.pylint.with({
-        -- Only used if available
-        condition = utils.is_executable_condition("pylint"),
-    })
-    null_ls.builtins.formatting.black.with({
-        extra_args = { "--fast" },
-        -- Only used if available
-        condition = utils.is_executable_condition("black"),
-    }),
-    null_ls.builtins.formatting.isort.with({
-        -- Only used if available
-        condition = utils.is_executable_condition("isort"),
-    }),
-})
-EOF
-
-" Change max length of a line to 88 for this buffer to match black's settings
-setlocal colorcolumn=88
-let b:undo_ftplugin.='|setlocal colorcolumn<'