Revert "Set correct OS for Android metrics"

This reverts commit 63f78e9c98ad4faeabca8e5151264f9d1244f30b.

Reason for revert: common.proto should not be changed in this repo.

Original change's description:
> Set correct OS for Android metrics
>
> Change-Id: I9767ec4bb86e4c67fd5d669b40b748f522f75984
> Reviewed-on: https://fuchsia-review.googlesource.com/c/cobalt/+/504604
> Reviewed-by: Maria Telyatnikova <wanderin@google.com>
> Reviewed-by: Jared Weinstein <jaredweinstein@google.com>
> Commit-Queue: Jared Weinstein <jaredweinstein@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ie2b535e3d706c37352898cc5fcd85dee308014a0
Reviewed-on: https://fuchsia-review.googlesource.com/c/cobalt/+/505778
Reviewed-by: Alexandre Zani <azani@google.com>
Reviewed-by: Cameron Dale <camrdale@google.com>
Commit-Queue: Alexandre Zani <azani@google.com>
diff --git a/src/pb/common.proto b/src/pb/common.proto
index c456cec..df3916f 100644
--- a/src/pb/common.proto
+++ b/src/pb/common.proto
@@ -2,6 +2,8 @@
 
 package cobalt;
 
+
+
 option java_multiple_files = true;
 option java_package = "com.google.cobalt";
 
@@ -31,7 +33,6 @@
     UNKNOWN_OS = 0;
     FUCHSIA = 1;
     LINUX = 2;
-    ANDROID = 3;
   }
 
   enum ARCH {
diff --git a/src/system_data/system_data.cc b/src/system_data/system_data.cc
index 85ccab1..70c5b13 100644
--- a/src/system_data/system_data.cc
+++ b/src/system_data/system_data.cc
@@ -181,10 +181,7 @@
 }
 
 void SystemData::PopulateSystemProfile() {
-#if defined(__ANDROID__)
-  system_profile_.set_os(SystemProfile::ANDROID);
-
-#elif defined(__linux__)
+#if defined(__linux__)
 
   system_profile_.set_os(SystemProfile::LINUX);