Replace StringFromInt with std::to_string

Updated version of #47. Android should support to_string now that
we use a modern version of libc++ when building.

Source/Core/Common/Config/Section.cpp

@@ -71,7 +71,7 @@ void Section::Set(const std::string& key, double newValue)
 
 void Section::Set(const std::string& key, int newValue)
 {
-  Section::Set(key, StringFromInt(newValue));
+  Section::Set(key, std::to_string(newValue));
 }
 
 void Section::Set(const std::string& key, bool newValue)

Source/Core/Common/IniFile.cpp

@@ -93,7 +93,7 @@ void IniFile::Section::Set(const std::string& key, double newValue)
 
 void IniFile::Section::Set(const std::string& key, int newValue)
 {
-  Set(key, StringFromInt(newValue));
+  Set(key, std::to_string(newValue));
 }
 
 void IniFile::Section::Set(const std::string& key, s64 newValue)

Source/Core/Common/StringUtil.cpp

@@ -283,13 +283,6 @@ bool TryParse(const std::string& str, bool* const output)
   return true;
 }
 
-std::string StringFromInt(int value)
-{
-  char temp[16];
-  sprintf(temp, "%i", value);
-  return temp;
-}
-
 std::string StringFromBool(bool value)
 {
   return value ? "True" : "False";

Source/Core/Common/StringUtil.h

@@ -56,7 +56,6 @@ std::string ThousandSeparate(I value, int spaces = 0)
   return oss.str();
 }
 
-std::string StringFromInt(int value);
 std::string StringFromBool(bool value);
 
 bool TryParse(const std::string& str, bool* output);