Remove the HTTP backend (#176)

The HTTP backend was mainly of use to talk to bazel-remote, but as far
as I know, that also supports gRPC perfectly fine nowadays. There is
absolutely no reason to prefer HTTP over gRPC. The latter supports doing
bulk existence checks, querying capabilities, while the former does not.

pkg/blobstore/BUILD.bazel

@@ -15,7 +15,6 @@ go_library(
         "existence_caching_blob_access.go",
         "fsac_read_buffer_factory.go",
         "hierarchical_instance_names_blob_access.go",
-        "http_blob_access.go",
         "icas_read_buffer_factory.go",
         "iscc_read_buffer_factory.go",
         "metrics_blob_access.go",

pkg/blobstore/configuration/new_blob_access.go

@@ -3,7 +3,6 @@ package configuration
 import (
 	"archive/zip"
 	"context"
-	"net/http"
 	"os"
 	"sync"
 	"time"
@@ -20,7 +19,6 @@ import (
 	"github.com/buildbarn/bb-storage/pkg/eviction"
 	"github.com/buildbarn/bb-storage/pkg/filesystem"
 	"github.com/buildbarn/bb-storage/pkg/grpc"
-	bb_http "github.com/buildbarn/bb-storage/pkg/http"
 	"github.com/buildbarn/bb-storage/pkg/program"
 	pb "github.com/buildbarn/bb-storage/pkg/proto/configuration/blobstore"
 	digest_pb "github.com/buildbarn/bb-storage/pkg/proto/configuration/digest"
@@ -85,22 +83,6 @@ func (nc *simpleNestedBlobAccessCreator) newNestedBlobAccessBare(configuration *
 			BlobAccess:      readcaching.NewReadCachingBlobAccess(slow.BlobAccess, fast.BlobAccess, replicator),
 			DigestKeyFormat: slow.DigestKeyFormat,
 		}, "read_caching", nil
-	case *pb.BlobAccessConfiguration_Http:
-		roundTripper, err := bb_http.NewRoundTripperFromConfiguration(backend.Http.Client)
-		if err != nil {
-			return BlobAccessInfo{}, "", util.StatusWrap(err, "Failed to create HTTP client")
-		}
-		return BlobAccessInfo{
-			BlobAccess: blobstore.NewHTTPBlobAccess(
-				backend.Http.Address,
-				storageTypeName,
-				readBufferFactory,
-				&http.Client{
-					Transport: bb_http.NewMetricsRoundTripper(roundTripper, "HTTPBlobAccess"),
-				},
-				creator.GetDefaultCapabilitiesProvider()),
-			DigestKeyFormat: digest.KeyWithInstance,
-		}, "remote", nil
 	case *pb.BlobAccessConfiguration_Sharding:
 		backends := make([]blobstore.BlobAccess, 0, len(backend.Sharding.Shards))
 		weights := make([]uint32, 0, len(backend.Sharding.Shards))