aix: Remove unnecessary library import that breaks build on PASE environment

Change-Id: Ifcd419601d090f5995feb064b017e813dcb00121
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2532878Reviewed-by: Milad Fa <mfarazma@redhat.com>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Vasili Skurydzin <vasili.skurydzin@ibm.com>
Cr-Commit-Position: refs/heads/master@{#71164}

BUILD.gn

@@ -4177,7 +4177,6 @@ v8_component("v8_libbase") {
 
     libs = [
       "dl",
-      "rt",
     ]
   } else if (is_android) {
     if (current_toolchain == host_toolchain) {