Removed {insert, extract}element and shufflevector pragmas.

They have been superseeded by the inline IR pragma and ldc.simd,
and have only been around for a short time (and not in any
released version).

dmd2/idgen.c

@@ -273,9 +273,6 @@ Msgtable msgtable[] =
     { "no_typeinfo" },
     { "no_moduleinfo" },
     { "Alloca", "alloca" },
-    { "Shufflevector", "shufflevector" },
-    { "Extractelement", "extractelement" },
-    { "Insertelement", "insertelement" },
     { "vastart", "va_start" },
     { "vacopy", "va_copy" },
     { "vaend", "va_end" },