cmd/coordinator/internal/lucipoll: update for new JSONPB field naming

As of crrev.com/c/5875121, golangbuild switched to the new default
behavior of using 'proto' field naming (such as "gitiles_commit")
instead of using protobuf default names (such as "gitilesCommit").

The previous behavior can still be achieved by explicitly using the
https://pkg.go.dev/go.chromium.org/luci/luciexe/build/properties#OptProtoUseJSONNames
option, but we choose to accept the new default behavior since it's
fine for our needs.

So, update a few places in lucipoll for the new field naming pattern
as was also recently done for watchflakes in CL 615515. Not handling
the old pattern here since lucipoll only needs to handle new builds.

Also drop the unused "omitempty" option from BuilderConfigProperties
while here - it's never used for marshaling, only unmarshaling.

For golang/go#69609.
For golang/go#65913.

Change-Id: Icf2f942fa9821f8781c9a2ecaddd2a3e10496ba2
Reviewed-on: https://go-review.googlesource.com/c/build/+/615976
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: David Chase <[email protected]>

cmd/coordinator/internal/lucipoll/lucipoll.go

@@ -36,13 +36,13 @@ type Builder struct {
 }
 
 type BuilderConfigProperties struct {
-	Repo     string `json:"project,omitempty"`
-	GoBranch string `json:"go_branch,omitempty"`
+	Repo     string `json:"project"`
+	GoBranch string `json:"go_branch"`
 	Target   struct {
-		GOOS   string `json:"goos,omitempty"`
-		GOARCH string `json:"goarch,omitempty"`
+		GOOS   string `json:"goos"`
+		GOARCH string `json:"goarch"`
 	} `json:"target"`
-	KnownIssue int `json:"known_issue,omitempty"`
+	KnownIssue int `json:"known_issue"`
 }
 
 type Build struct {
@@ -242,11 +242,11 @@ func runOnce(
 			var buildOutputProps struct {
 				Sources []struct {
 					GitilesCommit struct {
-						Project string
-						Ref     string
-						Id      string
-					}
-				}
+						Project string `json:"project"`
+						Ref     string `json:"ref"`
+						Id      string `json:"id"`
+					} `json:"gitiles_commit"`
+				} `json:"sources"`
 			}
 			if data, err := b.GetOutput().GetProperties().MarshalJSON(); err != nil {
 				return nil, nil, fmt.Errorf("marshaling build output properties to JSON failed: %v", err)
@@ -330,11 +330,11 @@ func runOnce(
 			var buildOutputProps struct {
 				Sources []struct {
 					GitilesCommit struct {
-						Project string
-						Ref     string
-						Id      string
-					}
-				}
+						Project string `json:"project"`
+						Ref     string `json:"ref"`
+						Id      string `json:"id"`
+					} `json:"gitiles_commit"`
+				} `json:"sources"`
 			}
 			if data, err := b.GetOutput().GetProperties().MarshalJSON(); err != nil {
 				return nil, nil, fmt.Errorf("marshaling build output properties to JSON failed: %v", err)