adb: shell: add -n flag to not read from stdin.

Shell scripts of the following form do not work properly with adb:
    echo "foo\nbar\nbaz" | {
        read FOO
        while [ "$FOO" != "" ]; do
            adb shell echo $FOO
            read FOO
        done
    }
The first run of adb shell will consume all of the contents of stdin,
causing the loop to immediately end. ssh solves this by providing a -n
flag that causes it to not read from stdin. This commit adds the same.

Bug: http://b/25817224
Change-Id: Id74ca62ef520bcf03678b50f4bf203916fd81038
diff --git a/adb/daemon/main.cpp b/adb/daemon/main.cpp
index f4e054e3..a56d1dc 100644
--- a/adb/daemon/main.cpp
+++ b/adb/daemon/main.cpp
@@ -34,6 +34,7 @@
 #include "adb.h"
 #include "adb_auth.h"
 #include "adb_listeners.h"
+#include "adb_utils.h"
 #include "transport.h"
 
 static const char* root_seclabel = nullptr;
@@ -217,16 +218,6 @@
     return 0;
 }
 
-static void close_stdin() {
-    int fd = unix_open("/dev/null", O_RDONLY);
-    if (fd == -1) {
-        perror("failed to open /dev/null, stdin will remain open");
-        return;
-    }
-    dup2(fd, STDIN_FILENO);
-    unix_close(fd);
-}
-
 int main(int argc, char** argv) {
     while (true) {
         static struct option opts[] = {