shill: OpenVPNDriver: Remove kOpenVPNMgmtEnableProperty

Since this argument isn't used in Chrome anymore, we are safe
to remove it from shill.

BUG=chromium:211858
TEST=Unit tests, network_VPNConnect.openvpn_user_pass, code search for
kOpenVPNMgmtEnableProperty in chrome.

Change-Id: I1ca7946e9430e60ae01a1a69a56686112aafa519
Reviewed-on: https://gerrit.chromium.org/gerrit/64293
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/openvpn_driver.cc b/openvpn_driver.cc
index baa7415..2ef1e7f 100644
--- a/openvpn_driver.cc
+++ b/openvpn_driver.cc
@@ -112,9 +112,6 @@
   { kOpenVPNTLSAuthProperty, 0 },
   { kOpenVPNVerbProperty, 0 },
   { kVPNMTUProperty, 0 },
-
-  // Provided only for compatibility.  crbug.com/211858
-  { flimflam::kOpenVPNMgmtEnableProperty, 0 },
 };
 
 const char OpenVPNDriver::kLSBReleaseFile[] = "/etc/lsb-release";