refactor: remove vendored Go repos, keep only .proto files

wfe-buildkit-protos/proto/github.com/moby/buildkit/solver/errdefs/errdefs.proto

@@ -0,0 +1,52 @@
+syntax = "proto3";
+
+package errdefs;
+
+option go_package = "github.com/moby/buildkit/solver/errdefs";
+
+import "github.com/moby/buildkit/solver/pb/ops.proto";
+
+message Vertex {
+	string digest = 1;
+}
+
+message Source {
+	pb.SourceInfo info = 1;
+	repeated pb.Range ranges = 2;
+}
+
+message Frontend {
+	string name = 1; // frontend name e.g. dockerfile.v0 or gateway.v0
+	string source = 2; // used by the gateway frontend to identify the source, which corresponds to the image name
+}
+
+message FrontendCap {
+	string name = 1;
+}
+
+message Subrequest {
+	string name = 1;
+}
+
+message Solve {
+	repeated string inputIDs = 1;
+	repeated string mountIDs = 2;
+	pb.Op op = 3;
+
+	oneof subject {
+		FileAction file = 4;
+		ContentCache cache = 5;
+	}
+
+	map<string, string> description = 6;
+}
+
+message FileAction {
+	// Index of the file action that failed the exec.
+	int64 index = 1;
+}
+
+message ContentCache {
+	// Original index of result that failed the slow cache calculation.
+	int64 index = 1;
+}