Remove spurious libclang-dev from zstd manifest

Summary: `libclang-dev` was listed as a deb dependency for the `zstd` fbcode_builder manifest, but `zstd` has no build-time dependency on libclang. This caused `libclang-dev` to be unexpectedly installed on Ubuntu 20.04+ systems that triggered the zstd manifest. Remove it.

Reviewed By: xiatingouyang

Differential Revision: D107766167

fbshipit-source-id: 45ed3eebdf6293574654e0e6ad89b96906e8b80d

Author: r-barnes

build/fbcode_builder/manifests/zstd

@@ -6,7 +6,6 @@ zstd
 
 # 18.04 zstd is too old
 [debs.not(all(distro=ubuntu,distro_vers="18.04"))]
-libclang-dev
 libzstd-dev
 zstd