Deprecate FLAGS_quic_use_std_cbrt.

net/quic/quic_flags.cc

Index: net/quic/quic_flags.cc
diff --git a/net/quic/quic_flags.cc b/net/quic/quic_flags.cc
index 5997e90e3bbed5b0692dedf45ac66e1362384ca8..77ae081f096563f7eaafc1b3008845ddc61ac7dc 100644
--- a/net/quic/quic_flags.cc
+++ b/net/quic/quic_flags.cc
@@ -41,9 +41,6 @@ bool FLAGS_quic_enable_bandwidth_resumption_experiment = true;
 // congestion control.
 bool FLAGS_quic_enable_pacing = false;
 
-// If true, use std::cbrt instead of custom cube root.
-bool FLAGS_quic_use_std_cbrt = true;
-
 // If true, then the source address tokens generated for QUIC connects will
 // store multiple addresses.
 bool FLAGS_quic_use_multiple_address_in_source_tokens = false;