Fix CQS signal. Id] 62183176 -- readability-redundant-string-init in fbcode/faiss/impl (#4332)

Differential Revision: D74239080

Pulled By: junjieqi

fbshipit-source-id: 635cb0f408168ab0ad1172965c5798767a23339c

Author: CodemodService Bot

faiss/impl/io.cpp

@@ -260,7 +260,7 @@ std::string fourcc_inv(uint32_t x) {
 std::string fourcc_inv_printable(uint32_t x) {
     char cstr[5];
     fourcc_inv(x, cstr);
-    std::string str = "";
+    std::string str;
     for (int i = 0; i < 4; i++) {
         uint8_t c = cstr[i];
         if (32 <= c && c < 127) {