Use update.py --package= instead of download_lld_mac.py and download_objdump.py

The separate download scripts for extra packages are going away and have been
replaced by update.py's new --package flag.

Bug: chromium:884608
Change-Id: I28f2f83a629a3fcda4a5524c10f9b10dd115e616
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1900462
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64813}

DEPS

@@ -486,14 +486,16 @@ hooks = [
     'name': 'lld/mac',
     'pattern': '.',
     'condition': 'host_os == "mac" and checkout_fuchsia',
-    'action': ['python', 'v8/tools/clang/scripts/download_lld_mac.py'],
+    'action': ['python', 'v8/tools/clang/scripts/update.py',
+               '--package=lld_mac'],
   },
   {
       # Mac does not have llvm-objdump, download it for cross builds in Fuchsia.
     'name': 'llvm-objdump',
     'pattern': '.',
     'condition': 'host_os == "mac" and checkout_fuchsia',
-    'action': ['python', 'v8/tools/clang/scripts/download_objdump.py'],
+    'action': ['python', 'v8/tools/clang/scripts/update.py',
+               '--package=objdump'],
   },
   # Download and initialize "vpython" VirtualEnv environment packages.
   {