Revert "Allow constructing String from std::variant<const char*,String>&&"

This reverts commit 5970c16.

Author: Al2Klimov

lib/base/string.cpp

@@ -37,15 +37,6 @@ String::String(String&& other) noexcept
 	: m_Data(std::move(other.m_Data))
 { }
 
-String::String(std::variant<const char*, String>&& data)
-{
-	if (auto str (std::get_if<String>(&data)); str) {
-		m_Data = std::move(str->m_Data);
-	} else {
-		m_Data = std::get<const char*>(data);
-	}
-}
-
 #ifndef _MSC_VER
 String::String(Value&& other)
 {

lib/base/string.hpp

@@ -11,7 +11,6 @@
 #include <functional>
 #include <string>
 #include <iosfwd>
-#include <variant>
 
 namespace icinga {
 
@@ -46,7 +45,6 @@ class String
 	String(String::SizeType n, char c);
 	String(const String& other);
 	String(String&& other) noexcept;
-	String(std::variant<const char*, String>&& data);
 
 #ifndef _MSC_VER
 	String(Value&& other);