Remove excessive constant declarations

When all .cc files are #included from a single master C++ file,
repetitive constant definitions - although the constant value remains
the same - makes MSVC error out.

Besides, it is not a good practice to redefine same constant over and
over again. It defies the main idea of constants: "define once, use
many times".

internal/getonescriptspan.cc

@@ -200,7 +200,6 @@ static const uint8 kTagParseTbl_0[] = {
 
 enum
 {
-  UTFmax        = 4,            // maximum bytes per rune
   Runesync      = 0x80,         // cannot represent part of a UTF sequence (<)
   Runeself      = 0x80,         // rune and UTF sequences are the same (<)
   Runeerror     = 0xFFFD,       // decoding error in UTF