Remove no longer used variable

Since 92961cd.

Author: nobu

ext/strscan/strscan.c

@@ -30,7 +30,6 @@ extern size_t onig_region_memsize(const struct re_registers *regs);
 
 static VALUE StringScanner;
 static VALUE ScanError;
-static ID id_byteslice;
 
 static int usascii_encindex, utf8_encindex, binary_encindex;
 
@@ -2287,8 +2286,6 @@ Init_strscan(void)
     ID id_scanerr = rb_intern("ScanError");
     VALUE tmp;
 
-    id_byteslice = rb_intern("byteslice");
-
     usascii_encindex = rb_usascii_encindex();
     utf8_encindex = rb_utf8_encindex();
     binary_encindex = rb_ascii8bit_encindex();