QHttpHeaders: remove unused Header::operator==()

The QHttpHeaders comparison was dropped earlier, and the current code
no longer needs to compare both header entry 'name' and 'value'.

Change-Id: I57a3003f0fd1d8ff867c970d5ec8a994a167ae88
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit c0e4b73743b9e9e8c3e116f9db9fe37bfcd89bf5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qhttpheaders.cpp

@@ -773,12 +773,6 @@ private:
 struct Header {
     HeaderName name;
     QByteArray value;
-
-private:
-    friend bool operator==(const Header &lhs, const Header &rhs) noexcept
-    {
-        return lhs.value == rhs.value && lhs.name == rhs.name;
-    }
 };
 
 auto headerNameMatches(const HeaderName &name)