Stop embedding soong_build_metrics in soong_metrics

Test: Run `m --bazel-mode-dev nothing` and query the database to make sure
soong_build_metrics will only update to its standalone column
Run `bp2build` and `b build` to make sure soong_build_metrics and
soong_metrics.soong_build_metrics will be null.

Bug: 262280865
Change-Id: Ice5115c468bda350b742c5a1d03fff66ad346cd6
diff --git a/ui/metrics/metrics_proto/metrics.proto b/ui/metrics/metrics_proto/metrics.proto
index 07a7df1..5ad13fc 100644
--- a/ui/metrics/metrics_proto/metrics.proto
+++ b/ui/metrics/metrics_proto/metrics.proto
@@ -93,7 +93,9 @@
   // The metrics for the whole build
   optional PerfInfo total = 21;
 
-  optional SoongBuildMetrics soong_build_metrics = 22;
+  // Deprecated because instead of embedding in a MetricsBase, we keep
+  // SoongBuildMetrics in its own file
+  optional SoongBuildMetrics soong_build_metrics = 22 [deprecated=true];
 
   optional BuildConfig build_config = 23;