Remove catch of critical PSERROR_Scripting exceptions in the GUI that is obsolete for the intended case and wrong for the unintended case.

The catch had been introduced in rP7285, seemingly to catch the case PSERROR_Scripting_LoadFile_OpenFailed from rP769 which was removed in rP14496, refs D2363.
The LoadGlobalScript and LoadGlobalScriptFile functions don't throw these errors unless that JS code calls broken C++ code throwing that.
In that case catching the error and continuing like nothing happened leads to subsequent segfaults and similarly severe errors caused by C++, not XML.

Differential Revision: https://code.wildfiregames.com/D2366
Tested on: clang 9.0.0, gcc 9.2.0, Jenkins/vs2015
Accepted By: nani