[gn] Fix "link" in the //examples/simple_build/build/toolchain/BUILD.gn

*.a files in the $out can not be removed because they are static library needed by the building step.
From the view of gn, `gn clean` is only standard way to clean up everything about output.

Change-Id: I473953ca0e4baf8ed6b5fa5dad3d2b55b7b9a67b
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/17181
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: David Turner <digit@google.com>
Reviewed-by: David Turner <digit@google.com>

examples/simple_build/build/toolchain/BUILD.gn

diff --git a/examples/simple_build/build/toolchain/BUILD.gn b/examples/simple_build/build/toolchain/BUILD.gn
index c04ee1e..e33e9ce 100644
--- a/examples/simple_build/build/toolchain/BUILD.gn
+++ b/examples/simple_build/build/toolchain/BUILD.gn
@@ -22,7 +22,7 @@
   }
 
   tool("alink") {
-    command = "rm -f {{output}} && ar rcs {{output}} {{inputs}}"
+    command = "ar rcs {{output}} {{inputs}}"
     description = "AR {{target_output_name}}{{output_extension}}"
 
     outputs =