Fix typo in configurationEditingMain.ts (microsoft#203970)

Removed the extra `an` in `The path where an an extension is installed`.

Author: charleprr

extensions/configuration-editing/src/configurationEditingMain.ts

@@ -67,7 +67,7 @@ function registerVariableCompletions(pattern: string): vscode.Disposable {
 					{ label: 'fileBasenameNoExtension', detail: vscode.l10n.t("The current opened file's basename with no file extension") },
 					{ label: 'defaultBuildTask', detail: vscode.l10n.t("The name of the default build task. If there is not a single default build task then a quick pick is shown to choose the build task.") },
 					{ label: 'pathSeparator', detail: vscode.l10n.t("The character used by the operating system to separate components in file paths. Is also aliased to '/'.") },
-					{ label: 'extensionInstallFolder', detail: vscode.l10n.t("The path where an an extension is installed."), param: 'publisher.extension' },
+					{ label: 'extensionInstallFolder', detail: vscode.l10n.t("The path where an extension is installed."), param: 'publisher.extension' },
 				].map(variable => ({
 					label: `\${${variable.label}}`,
 					range,