Bump linregress and do some other cleanups (#7580)

substrate/frame/benchmarking/Cargo.toml

@@ -13,7 +13,7 @@ readme = "README.md"
 targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
-linregress = "0.1"
+linregress = { version = "0.4.0", optional = true }
 paste = "0.1"
 codec = { package = "parity-scale-codec", version = "1.3.4", default-features = false }
 sp-api = { version = "2.0.0", path = "../../primitives/api", default-features = false }
@@ -38,4 +38,5 @@ std = [
 	"sp-std/std",
 	"frame-support/std",
 	"frame-system/std",
+	"linregress",
 ]