Rename time to event in Soong metrics system.

Several structs and files are named time which records the total
execution of a traceable event. Soon, resource information of an
executed process is collected during a build event so a more generic
name is applied.

Bug: b/169453825
Test: go test and m nothing. Checked the soong_metrics protobuf.
Change-Id: I65a782603530d51018d6cc1192c18cfeef7566a0
diff --git a/ui/metrics/Android.bp b/ui/metrics/Android.bp
index 8188a69..95c8f5c 100644
--- a/ui/metrics/Android.bp
+++ b/ui/metrics/Android.bp
@@ -23,10 +23,10 @@
     ],
     srcs: [
         "metrics.go",
-        "time.go",
+        "event.go",
     ],
     testSrcs: [
-        "time_test.go",
+        "event_test.go",
     ],
 }