ci: cleanup legacy R-loom-multi-thread-alt label from the labeler (#7457)

Signed-off-by: ADD-SP <[email protected]>

Author: ADD-SP

.github/labeler.yml

@@ -19,10 +19,3 @@ R-loom-multi-thread:
 - tokio/src/runtime/scheduler/multi_thread/**
 - tokio/src/runtime/task/*
 - tokio/src/runtime/task/**
-
-R-loom-multi-thread-alt:
-- tokio/src/runtime/scheduler/*
-- tokio/src/runtime/scheduler/multi_thread_alt/*
-- tokio/src/runtime/scheduler/multi_thread_alt/**
-- tokio/src/runtime/task/*
-- tokio/src/runtime/task/**