Fix up linting, make lint clean

Now that we are modules, there's no reason to ban multiple namespaces
per file; each file is its own scope and declaring a namespace won't
merge it into any other files.

scripts/eslint/rules/one-namespace-per-file.cjs

@@ -1,45 +0,0 @@
-const { AST_NODE_TYPES, TSESTree } = require("@typescript-eslint/utils");
-const { createRule } = require("./utils.cjs");
-
-module.exports = createRule({
-    name: "one-namespace-per-file",
-    meta: {
-        docs: {
-            description: `Limits each file to having at most one top-level namespace declaration`,
-            recommended: "error",
-        },
-        messages: {
-            excessNamespaceError: `All but one of these namespaces should be moved into separate files.`,
-        },
-        schema: [],
-        type: "problem",
-    },
-    defaultOptions: [],
-
-    create(context) {
-        /** @type {(node: TSESTree.Node) => node is TSESTree.TSModuleDeclaration} */
-        const isNamespaceDeclaration = (node) => node.type === AST_NODE_TYPES.TSModuleDeclaration;
-
-        /** @type {(node: TSESTree.Program) => void} */
-        const checkSourceFile = (node) => {
-            if (context.getFilename().endsWith(".d.ts")) {
-                return;
-            }
-            const members = node.body;
-            const namespaces = members.filter(isNamespaceDeclaration);
-            if (namespaces.length <= 1) {
-                return;
-            }
-
-            namespaces.forEach(n => {
-                context.report({
-                    messageId: "excessNamespaceError", node: n
-                });
-            });
-        };
-
-        return {
-            Program: checkSourceFile,
-        };
-    },
-});