Remove hardcoded qt_instdate field from binary

Move hardcoded date to the only client code in the repo.

This field is currently modified by MaintenanceTool and possibly windeployqt,
which contributes to breaking the DLL signature on Windows. Removing the field
should avoid this problem.

Task-number: QTBUG-76985
Change-Id: I01386136ac493ea50c99c05879a3e215f3f6344c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

configure.pri

@@ -835,9 +835,6 @@ defineTest(qtConfOutput_preparePaths) {
     addConfStr($$[QMAKE_SPEC])
 
     $${currentConfig}.output.qconfigSource = \
-        "/* Installation date */" \
-        "static const char qt_configure_installation     [12+11]  = \"qt_instdate=2012-12-20\";" \
-        "" \
         "/* Installation Info */" \
         "static const char qt_configure_prefix_path_str  [12+256] = \"qt_prfxpath=$$config.input.prefix\";" \
         "$${LITERAL_HASH}ifdef QT_BUILD_QMAKE" \

src/corelib/global/qlibraryinfo.cpp

@@ -274,7 +274,7 @@ QLibraryInfo::licensedProducts()
 QDate
 QLibraryInfo::buildDate()
 {
-    return QDate::fromString(QString::fromLatin1(qt_configure_installation + 12), Qt::ISODate);
+    return QDate::fromString(QString::fromLatin1("2012-12-20"), Qt::ISODate);
 }
 #endif
 #endif // datestring