Kill WTF::GregorianDateTime class

Source/wtf/wtf.gypi

 # For GN compatibility, this file can not have any conditions.
 {
     'variables': {
         'wtf_files': [
             'ASCIICType.h',
             'Alignment.h',
             'ArrayBuffer.cpp',
             'ArrayBuffer.h',
             'ArrayBufferBuilder.cpp',
             'ArrayBufferBuilder.h',
@@ skipping 37 matching lines @@
             'FastAllocBase.h',
             'FastMalloc.cpp',
             'FastMalloc.h',
             'FilePrintStream.cpp',
             'FilePrintStream.h',
             'Float32Array.h',
             'Float64Array.h',
             'Forward.h',
             'Functional.h',
             'GetPtr.h',
-            'GregorianDateTime.cpp',
-            'GregorianDateTime.h',
             'HashCountedSet.h',
             'HashFunctions.h',
             'HashIterators.h',
             'HashMap.h',
             'HashSet.h',
             'HashTable.cpp',
             'HashTable.h',
             'HashTableDeletedValueType.h',
             'HashTraits.h',
             'HexNumber.h',
@@ skipping 164 matching lines @@
             'text/TextCodecUTF8Test.cpp',
             'text/WTFStringTest.cpp',
         ],
         'wtf_unittest_helper_files': [
             'testing/WTFTestHelpers.cpp',
             'testing/WTFTestHelpers.h',
             'testing/WTFUnitTestHelpersExport.h',
         ],
     },
 }