Revert "adb: add support for O_CLOEXEC to unique_fd pipe wrapper."

This reverts commit 948b3e1068470cda390566452ccbaeb526a56e4e.

Reason for revert: mac doesn't have pipe2

Change-Id: Id6a517bb500cbea602839f06452bc5e6d92289f1
diff --git a/adb/adb_unique_fd.h b/adb/adb_unique_fd.h
index 0dd8687..9c02cbe 100644
--- a/adb/adb_unique_fd.h
+++ b/adb/adb_unique_fd.h
@@ -28,9 +28,9 @@
 using unique_fd = android::base::unique_fd_impl<AdbCloser>;
 
 #if !defined(_WIN32)
-inline bool Pipe(unique_fd* read, unique_fd* write, int flags = 0) {
+inline bool Pipe(unique_fd* read, unique_fd* write) {
     int pipefd[2];
-    if (pipe2(pipefd, flags) != 0) {
+    if (pipe(pipefd) != 0) {
         return false;
     }
     read->reset(pipefd[0]);