Remove use_system_ssl GYP flag

It's no longer supported. Packagers that wish to replace how Chromium
packages/uses NSS should add support via src/build/linux/unbundle

BUG=336511
R=phajdan.jr, brettw

Review URL: https://codereview.chromium.org/139743009

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 516009142bfa85a27b5c50a700bd3fa1e02f8dc6
diff --git a/tools/gn/secondary/crypto/ssl/BUILD.gn b/tools/gn/secondary/crypto/ssl/BUILD.gn
index dc78efc..0cb3ce0 100644
--- a/tools/gn/secondary/crypto/ssl/BUILD.gn
+++ b/tools/gn/secondary/crypto/ssl/BUILD.gn
@@ -13,14 +13,6 @@
   }
 }
 
-# Config for system SSL on Linux.
-if (is_linux && use_system_ssl) {
-  pkg_config("system_ssl_config") {
-    packages = [ "nss" ]
-    defines = [ "USE_SYSTEM_SSL" ]
-  }
-}
-
 # This meta-target will include the SSL library according to the build flags.
 group("metassl") {
   direct_dependent_configs = [ ":ssl_preprocessor_flags" ]
@@ -29,9 +21,6 @@
     assert(is_linux)
     deps = "//third_party/openssl"
     use_openssl = false
-  } else if (use_system_ssl) {
-    assert(is_linux)
-    direct_dependent_configs = ":system_ssl_config"
   } else {
     deps = [ "//net/third_party/nss:ssl" ]
   }
diff --git a/tools/gn/secondary/crypto/ssl/flags.gni b/tools/gn/secondary/crypto/ssl/flags.gni
index aac6e96..6891c49 100644
--- a/tools/gn/secondary/crypto/ssl/flags.gni
+++ b/tools/gn/secondary/crypto/ssl/flags.gni
@@ -8,9 +8,6 @@
   # Use OpenSSL instead of NSS. This is used for Android and is experimental
   # in other cases (see http://crbug.com/62803).
   use_openssl = false
-
-  # Use the built-in system SSL library rather than our tree's libnss/OpenSSL.
-  use_system_ssl = false
 }
 
 if (is_linux && !use_openssl) {