Terminal: Remove TOO_OLD_WINSDK check from libptyqt

Qt Creator will always use newer Windows SDKs, as we require at least
Windows 10 1809.

The define for TOO_OLD_WINSDK was done arbitrarily and broke
(LLVM-)MinGW builds.

Change-Id: If8e1fd4e0e3615bda23483877e67988ca04ea9f7
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/3rdparty/libptyqt/conptyprocess.cpp

@@ -1132,10 +1132,6 @@ qint64 ConPtyProcess::write(const QByteArray &byteArray)
 
 bool ConPtyProcess::isAvailable()
 {
-#ifdef TOO_OLD_WINSDK
-    return false; //very importnant! ConPty can be built, but it doesn't work if built with old sdk and Win10 < 1903
-#endif
-
     qint32 buildNumber = QSysInfo::kernelVersion().split(".").last().toInt();
     if (buildNumber < CONPTY_MINIMAL_WINDOWS_VERSION)
         return false;

src/libs/3rdparty/libptyqt/conptyprocess.h

@@ -20,7 +20,6 @@
 
 typedef VOID* HPCON;
 
-#define TOO_OLD_WINSDK
 #endif
 
 class QWinEventNotifier;