Fix string_view constructor for macOS clang

Some versions of clang 14 (macOS+android) don't implement
`string_view(It first, It last)`, so let's use
`string_view(const CharT*, size_type)` instead.

Also remove unused header leftover from old code that uses std::string.

src/core/gdbstub/hio.cpp

@@ -81,8 +81,8 @@ void SetHioRequest(const VAddr addr) {
 
     if (current_hio_request.magic != std::array{'G', 'D', 'B', '\0'}) {
         std::string_view bad_magic{
-            std::begin(current_hio_request.magic),
-            std::end(current_hio_request.magic),
+            current_hio_request.magic.data(),
+            current_hio_request.magic.size(),
         };
         LOG_WARNING(Debug_GDBStub, "Invalid HIO request sent by application: bad magic '{}'",
                     bad_magic);

src/core/gdbstub/hio.h

@@ -4,8 +4,6 @@
 
 #pragma once
 
-#include <string>
-
 #include "common/common_types.h"
 
 namespace GDBStub {