[eslint-plugin] update stub typings to use modern syntax (#36747)

and remove typings for dependencies that we removed already.

Author: jeremymeng

common/tools/eslint-plugin-azure-sdk/src/typings/eslint-plugin-import.d.ts

@@ -1,6 +1,6 @@
 declare module 'eslint-plugin-no-only-tests' {
   import type { FixupPluginDefinition } from '@eslint/compat';
 
-  declare const exprt: FixupPluginDefinition;
-  export = exprt;
+  const exprt: FixupPluginDefinition;
+  export default exprt;
 }

common/tools/eslint-plugin-azure-sdk/src/typings/eslint-plugin-markdown.d.ts

@@ -1,12 +1,12 @@
 declare module 'eslint-plugin-promise' {
   import type { FlatConfig } from '@typescript-eslint/utils/ts-eslint';
 
-  declare const exprt: {
+  const exprt: {
     meta: FlatConfig.PluginMeta,
     plugin: FlatConfig.Plugin,
     configs: {
       "flat/recommended": FlatConfig.Config;
     };
   };
-  export = exprt;
+  export default exprt;
 }