build: remove cxx and cxx-bridge

Temporarily removed `cxx` and `cxx-bridge` due to an issue where `cxx-bridge`
attempts to create a directory in a read-only file system when importing in
Tachyon. This causes a build failure with the following error message:

```shell
ERROR: /home/chokobole/.cache/bazel/_bazel_chokobole/234690e3562329d13f7f07caac03dae4/external/crate_index__halo2_proofs-1.1.0/BUILD.bazel:113:19: Running Cargo build script halo2_proofs failed: (Exit 1): cargo_build_script_runner failed: error executing command (from target @crate_index__halo2_proofs-1.1.0//:halo2_proofs_build_script) bazel-out/k8-opt-exec-2B5CBBC6/bin/external/rules_rust/cargo/cargo_build_script_runner/cargo_build_script_runner ... (remaining 11 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
Build script process failed with exit code 1
--stdout:

--stderr:

cxxbridge error: Failed to create directory `/home/chokobole/.cache/bazel/_bazel_chokobole/234690e3562329d13f7f07caac03dae4/sandbox/linux-sandbox/6005/execroot/kroma_network_tachyon/bazel-out/k8-opt-exec-2B5CBBC6/bin/external/crate_index__scratch-1.0.7/scratch_build_script.out_dir/cxxbridge/rust`

Caused by:
    Read-only file system (os error 30)
```

halo2_proofs/Cargo.toml

@@ -75,9 +75,6 @@ log = "0.4.17"
 # timer
 ark-std = { version = "0.3.0" }
 
-# binding
-cxx = "1.0.122"
-
 # Legacy circuit compatibility
 halo2_legacy_pdqsort = { version = "0.1.0", optional = true }
 
@@ -92,9 +89,6 @@ rand_core = { version = "0.6", default-features = false, features = [
 ] }
 rand_xorshift = "0.3"
 
-[build-dependencies]
-cxx-build = "1.0.122"
-
 [target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dev-dependencies]
 getrandom = { version = "0.2", features = ["js"] }