Remove QuicString wrapper for std::string

gfe-relnote: n/a (no functional change)
PiperOrigin-RevId: 238124961
Change-Id: I36e66a4326b4118d70effd356aef9734d2893763

quic/core/crypto/proof_source.h

diff --git a/quic/core/crypto/proof_source.h b/quic/core/crypto/proof_source.h
index 0f293be..cc777c7 100644
--- a/quic/core/crypto/proof_source.h
+++ b/quic/core/crypto/proof_source.h
@@ -6,6 +6,7 @@
 #define QUICHE_QUIC_CORE_CRYPTO_PROOF_SOURCE_H_
 
 #include <memory>
+#include <string>
 #include <vector>
 
 #include "net/third_party/quiche/src/quic/core/crypto/quic_crypto_proof.h"
@@ -13,7 +14,6 @@
 #include "net/third_party/quiche/src/quic/platform/api/quic_export.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_reference_counted.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_socket_address.h"
-#include "net/third_party/quiche/src/quic/platform/api/quic_string.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_string_piece.h"
 
 namespace quic {