build: remove useless build scripts (copy & paste artifact)

This will also prevent some useless rebuilds. Using `--verbose` we can
observe that the build.rs causes frequent useless rebuilds - having
less is a good thing. They come from the dependency of `build.rs` to
the local git repository.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

performance-metrics/Cargo.toml

@@ -1,6 +1,5 @@
 [package]
 authors = ["The Cloud Hypervisor Authors"]
-build = "../build.rs"
 edition.workspace = true
 name = "performance-metrics"
 version = "0.1.0"

vhost_user_block/Cargo.toml

@@ -1,6 +1,5 @@
 [package]
 authors = ["The Cloud Hypervisor Authors"]
-build = "../build.rs"
 edition.workspace = true
 name = "vhost_user_block"
 version = "0.1.0"

vhost_user_net/Cargo.toml

@@ -1,6 +1,5 @@
 [package]
 authors = ["The Cloud Hypervisor Authors"]
-build = "../build.rs"
 edition.workspace = true
 name = "vhost_user_net"
 version = "0.1.0"