tools/battor_agent: Removes CrOS and Android from target platforms

https://crrev.com/1611533002/ added necessary serial device enumeration
to the agent, which broke the Android build because I was inadvertently
building the agent on Android builders.

My goal is to have battor_agent only be buildable on Mac, Windows, and
Linux desktop machines. If I did that wrong, please let me know!

Review URL: https://codereview.chromium.org/1611353003

Cr-Commit-Position: refs/heads/master@{#371367}
diff --git a/BUILD.gn b/BUILD.gn
index ca463989..91b0c0a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -148,6 +148,7 @@
       "//third_party/cacheinvalidation:cacheinvalidation_unittests",
       "//third_party/codesighs",
       "//third_party/pdfium/samples:pdfium_test",
+      "//tools/battor_agent",
       "//tools/gn",
       "//tools/gn:gn_unittests",
       "//tools/perf/clear_system_cache",
@@ -222,10 +223,6 @@
     }
   }
 
-  if (is_mac || is_win || is_linux) {
-    deps += [ "//tools/battor_agent" ]
-  }
-
   deps += root_extra_deps
 
   if (enable_extensions) {