Remove type declarations where not yet possible

Because we don't return consistent things yet :(

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/public/User/Backend/ICheckPasswordBackend.php

@@ -31,5 +31,5 @@ interface ICheckPasswordBackend {
 	/**
 	 * @since 14.0.0
 	 */
-	public function checkPassword(string $loginName, string $password): string;
+	public function checkPassword(string $loginName, string $password);
 }

lib/public/User/Backend/ICountUsersBackend.php

@@ -32,5 +32,5 @@ interface ICountUsersBackend {
 	/**
 	 * @since 14.0.0
 	 */
-	public function countUsers(): int;
+	public function countUsers();
 }

lib/public/User/Backend/IGetDisplayNameBackend.php

@@ -32,5 +32,5 @@ interface IGetDisplayNameBackend {
 	/**
 	 * @since 14.0.0
 	 */
-	public function getDisplayName(string $uid): string;
+	public function getDisplayName($uid): string;
 }

lib/public/User/Backend/IGetHomeBackend.php

@@ -32,5 +32,5 @@ interface IGetHomeBackend {
 	/**
 	 * @since 14.0.0
 	 */
-	public function getHome(string $uid): string;
+	public function getHome(string $uid);
 }