Regenerate all BUILD files in vendor/ from scratch using gazelle

vendor/github.com/grpc-ecosystem/go-grpc-prometheus/BUILD

@@ -1,9 +1,4 @@
-package(default_visibility = ["//visibility:public"])
-
-load(
-    "@io_bazel_rules_go//go:def.bzl",
-    "go_library",
-)
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
@@ -14,6 +9,7 @@ go_library(
         "server_reporter.go",
         "util.go",
     ],
+    visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/prometheus/client_golang/prometheus:go_default_library",
         "//vendor/golang.org/x/net/context:go_default_library",
@@ -33,4 +29,5 @@ filegroup(
     name = "all-srcs",
     srcs = [":package-srcs"],
     tags = ["automanaged"],
+    visibility = ["//visibility:public"],
 )