Remove libclang pin from clang dependency group

The explicit libclang==20.1.8 pin causes the conda solver to hang when
combined with matplotlib (which pulls in Qt6, which requires
libclang13>=22.1.0). The solver cannot efficiently resolve the conflict
between the pinned older libclang and Qt6's newer requirement, leading
to effectively infinite solve times in environments with many packages
(such as the combined RAPIDS devcontainer environment).

The libclang package is not needed in the clang dependency group:
- clang and clang-tools do not depend on libclang
- The Rust bindgen workflow (the original reason libclang was added)
  uses the rust file key which does not include the clang group
- bindgen finds libclang.so at runtime from whatever version is
  available in the environment (provided transitively by Qt/matplotlib)

Other RAPIDS repos (cudf, raft, rmm) only pin clang and clang-tools
without libclang and do not experience this issue.

Author: vyasr

conda/environments/all_cuda-129_arch-aarch64.yaml

@@ -22,7 +22,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-aarch64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/all_cuda-129_arch-x86_64.yaml

@@ -22,7 +22,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/all_cuda-133_arch-aarch64.yaml

@@ -22,7 +22,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-aarch64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/all_cuda-133_arch-x86_64.yaml

@@ -22,7 +22,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/bench_ann_cuda-129_arch-aarch64.yaml

@@ -24,7 +24,6 @@ dependencies:
 - gcc_linux-aarch64=14.*
 - glog>=0.6.0
 - h5py>=3.8.0
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/bench_ann_cuda-129_arch-x86_64.yaml

@@ -26,7 +26,6 @@ dependencies:
 - h5py>=3.8.0
 - libaio
 - libboost-devel=1.87
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/bench_ann_cuda-133_arch-aarch64.yaml

@@ -24,7 +24,6 @@ dependencies:
 - gcc_linux-aarch64=14.*
 - glog>=0.6.0
 - h5py>=3.8.0
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/bench_ann_cuda-133_arch-x86_64.yaml

@@ -26,7 +26,6 @@ dependencies:
 - h5py>=3.8.0
 - libaio
 - libboost-devel=1.87
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/go_cuda-129_arch-aarch64.yaml

@@ -20,7 +20,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-aarch64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev

conda/environments/go_cuda-129_arch-x86_64.yaml

@@ -20,7 +20,6 @@ dependencies:
 - dlpack>=0.8,<1.0
 - gcc_linux-64=14.*
 - go
-- libclang==20.1.8
 - libcublas-dev
 - libcurand-dev
 - libcusolver-dev