wdk-build: The `signtool-sign` build process requires network connection for a little value

[tandasat]

The signtool-sign build process executes signtool with the /t flag. This requires network connection every time, which is inconvenient for offline work.

windows-drivers-rs/crates/wdk-build/rust-driver-makefile.toml

Lines 475 to 484 in 547b792

	command = "signtool"
	args = [
	"sign",
	"/v",
	"/s",
	"WDRTestCertStore", # FIXME: this should be a parameter
	"/n",
	"WDRLocalTestCert", # FIXME: this should be a parameter
	"/t",
	"http://timestamp.digicert.com",

I propose to remove this flag.

While specifying /t is not inherently a bad idea, the benefit of that with wdk-build is effectively none given signing with this project is done with merely WDRLocalTestCert and not meant for production releases. In other words, while adding a timestamp with /t keeps the signature valid even after the certificate has expired (ref), but practically no one would care about this situation, put aside that it has a quite long validity (15 years on my env). If they do care, they would be signing with their own certs and commands like requested in #588. So, overall, invoking signtool with /t only makes the use of this project difficult with no practical value.