Remove about:flags#enable-spdy4 flag.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 3733ee7a200f08230244a64ed899cde9f8f2d35a..ff5272c1c351eda1ee4d194fb08d939e3a0a8b2d 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6007,11 +6007,11 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_QUIC_DESCRIPTION" desc="Description for the flag to enable QUIC.">
         Enable experimental QUIC protocol support.
       </message>
-      <message name="IDS_FLAGS_ENABLE_SPDY4_NAME" desc="Title for the flag to enable SPDY/4">
-        Enable SPDY/4
+      <message name="IDS_FLAGS_ENABLE_SPDY4_NAME" desc="Title for the flag to enable HTTP/2">
+        Enable HTTP/2
       </message>
-      <message name="IDS_FLAGS_ENABLE_SPDY4_DESCRIPTION" desc="Description for the flag to enable SPDY/4.">
-        Enable SPDY/4, which is the HTTP/2 standard. Currently experimental.
+      <message name="IDS_FLAGS_ENABLE_SPDY4_DESCRIPTION" desc="Description for the flag to enable HTTP/2.">
+        Enable HTTP/2 and SPDY/3.1 protocols.
       </message>
       <message name="IDS_FLAGS_DISABLE_MEDIA_SOURCE_NAME" desc="Title for the flag to disable the Media Source API.">
         Disable Media Source API.