Drop old expat sources to make room for a fresh import

Utilities/cmexpat/.NoDartCoverage

Utilities/cmexpat/CMakeLists.txt

Utilities/cmexpat/COPYING

Utilities/cmexpat/ascii.h

Utilities/cmexpat/asciitab.h

Utilities/cmexpat/cm_expat_mangle.h

Utilities/cmexpat/expat.h

Utilities/cmexpat/expatConfig.h.in

Utilities/cmexpat/expatDllConfig.h.in

Utilities/cmexpat/iasciitab.h

Utilities/cmexpat/latin1tab.h

Utilities/cmexpat/nametab.h

Utilities/cmexpat/utf8tab.h

Utilities/cmexpat/xmlparse.c

Utilities/cmexpat/xmlrole.c

Utilities/cmexpat/xmlrole.h

Utilities/cmexpat/xmltok.c

Utilities/cmexpat/xmltok.h

Utilities/cmexpat/xmltok_impl.c

Utilities/cmexpat/xmltok_impl.h