Remove override specifier from function definition 'EMICostume::restoreS...

When compiling with C++11 code enabled, GCC 4.7.2 reports the following error:

    engines/grim/emi/costumeemi.cpp:237:48: error: virt-specifiers in ‘restoreState’ not allowed outside a class definition

Fixed simply by removing the override specified from the function definition, leaving the header file unchanged.