http: simplify connection: close search

Remove upgrade from the regular expression as it is no longer used
and switch to using `.test()` instead of `.match()` as the value
matched is irrelevant.

PR-URL: #20131
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/_http_outgoing.js

@@ -52,7 +52,7 @@ const { utcDate } = internalHttp;
 
 const kIsCorked = Symbol('isCorked');
 
-var RE_CONN_VALUES = /(?:^|\W)close|upgrade(?:$|\W)/ig;
+var RE_CONN_CLOSE = /(?:^|\W)close(?:$|\W)/i;
 var RE_TE_CHUNKED = common.chunkExpression;
 
 // isCookieField performs a case-insensitive comparison of a provided string
@@ -432,28 +432,17 @@ function storeHeader(self, state, key, value, validate) {
   matchHeader(self, state, key, value);
 }
 
-function matchConnValue(self, state, value) {
-  var sawClose = false;
-  var m = RE_CONN_VALUES.exec(value);
-  while (m) {
-    if (m[0].length === 5)
-      sawClose = true;
-    m = RE_CONN_VALUES.exec(value);
-  }
-  if (sawClose)
-    self._last = true;
-  else
-    self.shouldKeepAlive = true;
-}
-
 function matchHeader(self, state, field, value) {
   if (field.length < 4 || field.length > 17)
     return;
   field = field.toLowerCase();
   switch (field) {
     case 'connection':
       state.connection = true;
-      matchConnValue(self, state, value);
+      if (RE_CONN_CLOSE.test(value))
+        self._last = true;
+      else
+        self.shouldKeepAlive = true;
       break;
     case 'transfer-encoding':
       state.te = true;