Remove detritus

- rustfmt settings are hierarchical.
- integration-ebpf is always compiled at a distance with flags provided.
- .cargo/config.toml is not respected except at the root of the
  workspace[0].

[0] https://doc.rust-lang.org/cargo/reference/config.html#hierarchical-structure

bpf/.cargo/config.toml

@@ -1,6 +0,0 @@
-[build]
-target-dir = "../target"
-target = "bpfel-unknown-none"
-
-[unstable]
-build-std = ["core"]

test/integration-ebpf/.cargo/config.toml

@@ -1,6 +0,0 @@
-[build]
-target-dir = "../../target"
-target = "bpfel-unknown-none"
-
-[unstable]
-build-std = ["core"]

test/integration-ebpf/rust-toolchain.toml

@@ -1,2 +0,0 @@
-[toolchain]
-channel="nightly"

test/integration-ebpf/rustfmt.toml

@@ -1 +0,0 @@
-../../rustfmt.toml