tests/thread_flags: exchange printf with puts

tests/thread_flags/main.c

@@ -29,24 +29,24 @@ static void *_thread(void *arg)
 
     thread_flags_t flags;
 
-    printf("thread(): waiting for 0x1...\n");
+    puts("thread(): waiting for 0x1...");
     flags = thread_flags_wait_any(0x1);
     printf("thread(): received flags: 0x%04x\n", (unsigned)flags & 0xFFFF);
 
-    printf("thread(): waiting for 0x1 || 0x64...\n");
+    puts("thread(): waiting for 0x1 || 0x64...");
     flags = thread_flags_wait_any(0x1 | 0x64);
     printf("thread(): received flags: 0x%04x\n", (unsigned)flags & 0xFFFF);
 
-    printf("thread(): waiting for 0x2 && 0x4...\n");
+    puts("thread(): waiting for 0x2 && 0x4...");
     flags = thread_flags_wait_all(0x2 | 0x4);
     printf("thread(): received flags: 0x%04x\n", (unsigned)flags & 0xFFFF);
 
 
-    printf("thread(): waiting for any flag, one by one\n");
+    puts("thread(): waiting for any flag, one by one");
     flags = thread_flags_wait_one(0xFFFF);
     printf("thread(): received flags: 0x%04x\n", (unsigned)flags & 0xFFFF);
 
-    printf("thread(): waiting for any flag, one by one\n");
+    puts("thread(): waiting for any flag, one by one");
     flags = thread_flags_wait_one(0xFFFF);
     printf("thread(): received flags: 0x%04x\n", (unsigned)flags & 0xFFFF);
 
@@ -61,7 +61,7 @@ static void _set(thread_t *thread, thread_flags_t flags)
 
 int main(void)
 {
-    printf("main starting\n");
+    puts("main starting");
 
     kernel_pid_t pid = thread_create(stack,
                   sizeof(stack),