remove using namespace std and use std namespace explicitly (#2125)

Removes `using namespace std` and adds `std::` explicitly instead, which
is usually on calls to `min`.

This is generally best practice, and it also might be helpful when there
are the same function names in the std namespace and in the global
namespace (e.g. #1833).

test_conformance/api/test_clone_kernel.cpp

@@ -20,8 +20,6 @@
 #include <string>
 #include <cmath>
 
-using namespace std;
-
 const char *clone_kernel_test_img[] =
 {
     "__kernel void img_read_kernel(read_only image2d_t img, sampler_t sampler, __global int* outbuf)\n"

test_conformance/api/test_queue_hint.cpp

@@ -19,11 +19,6 @@
 #include <sstream>
 #include <string>
 
-using namespace std;
-/*
-
-*/
-
 const char *queue_hint_test_kernel[] = {
 "__kernel void vec_cpy(__global int *src, __global int *dst)\n"
 "{\n"

test_conformance/api/test_queue_properties.cpp

@@ -22,7 +22,6 @@
 #include <string>
 #include <vector>
 
-using namespace std;
 /*
 The test against cl_khr_create_command_queue extension. It validates if devices with Opencl 1.X can use clCreateCommandQueueWithPropertiesKHR function.
 Based on device capabilities test will create queue with NULL properties, CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE property and