all: rename tag and flags for legacy support

Rename build tag "proto1_legacy" -> "protolegacy"
to be consistent with the "protoreflect" tag.

Rename flag constant "Proto1Legacy" -> "ProtoLegacy" since
it covers more than simply proto1 legacy features.
For example, it covers alpha-features of proto3 that
were eventually removed from the final proto3 release.

Change-Id: I0f4fcbadd4b5a61c87645e2e5be11d187e59157c
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/189345
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/encoding/protojson/decode_test.go b/encoding/protojson/decode_test.go
index 9c4f93e..c343104 100644
--- a/encoding/protojson/decode_test.go
+++ b/encoding/protojson/decode_test.go
@@ -1334,7 +1334,7 @@
 			})
 			return m
 		}(),
-		skip: !flags.Proto1Legacy,
+		skip: !flags.ProtoLegacy,
 	}, {
 		desc:         "not real MessageSet 1",
 		inputMessage: &pb2.FakeMessageSet{},
@@ -1350,7 +1350,7 @@
 			})
 			return m
 		}(),
-		skip: !flags.Proto1Legacy,
+		skip: !flags.ProtoLegacy,
 	}, {
 		desc:         "not real MessageSet 2",
 		inputMessage: &pb2.FakeMessageSet{},
@@ -1360,7 +1360,7 @@
   }
 }`,
 		wantErr: true,
-		skip:    !flags.Proto1Legacy,
+		skip:    !flags.ProtoLegacy,
 	}, {
 		desc:         "not real MessageSet 3",
 		inputMessage: &pb2.MessageSet{},
@@ -1376,7 +1376,7 @@
 			})
 			return m
 		}(),
-		skip: !flags.Proto1Legacy,
+		skip: !flags.ProtoLegacy,
 	}, {
 		desc:         "Empty",
 		inputMessage: &emptypb.Empty{},
@@ -2457,13 +2457,13 @@
 			m.SetWeakMessage1(&weakpb.WeakImportMessage1{A: proto.Int32(1)})
 			return m
 		}(),
-		skip: !flags.Proto1Legacy,
+		skip: !flags.ProtoLegacy,
 	}, {
 		desc:         "weak fields; unknown field",
 		inputMessage: &testpb.TestWeak{},
 		inputText:    `{"weak_message1":{"a":1}, "weak_message2":{"a":1}}`,
 		wantErr:      true, // weak_message2 is unknown since the package containing it is not imported
-		skip:         !flags.Proto1Legacy,
+		skip:         !flags.ProtoLegacy,
 	}}
 
 	for _, tt := range tests {