Revert "net/tlsdial: add memory-optimized TLS cert verification path for iOS"

This reverts commit 6fcbd4c4d4.

Decided to put it in tailscale/go's crypto/x509 instead.

net/tlsdial/tlsdial.go

@@ -8,8 +8,6 @@ package tlsdial
 
 import "crypto/tls"
 
-var platformModifyConf func(*tls.Config)
-
 // Config returns a tls.Config for dialing the given host.
 // If base is non-nil, it's cloned as the base config before
 // being configured and returned.
@@ -22,9 +20,5 @@ func Config(host string, base *tls.Config) *tls.Config {
 	}
 	conf.ServerName = host
 
-	if platformModifyConf != nil {
-		platformModifyConf(conf)
-	}
-
 	return conf
 }