src: remove unused variable from string_search.h

PR-URL: #25139
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: addaleax

src/string_search.h

@@ -14,8 +14,6 @@
 namespace node {
 namespace stringsearch {
 
-static const uint32_t kMaxOneByteCharCodeU = 0xff;
-
 template <typename T>
 class Vector {
  public: