[easy][antlir] more dead code in build_defs (facebookincubator#215)

Summary:

You gotta be kidding me

Test Plan:
```
❯ buck targets fbcode//antlir/...
```

Differential Revision: D53968022

antlir/bzl/build_defs.bzl

@@ -255,17 +255,14 @@ buck_filegroup = shim.buck_filegroup
 buck_genrule = shim.buck_genrule
 buck_sh_binary = shim.buck_sh_binary
 buck_sh_test = shim.buck_sh_test
-buck_worker_tool = shim.buck_worker_tool
 config = shim.config
 export_file = shim.export_file
 get_visibility = shim.get_visibility
 http_file = shim.http_file
 http_archive = shim.http_archive
 is_buck2 = shim.is_buck2
 is_facebook = shim.is_facebook
-get_cxx_platform_for_current_buildfile = shim.get_cxx_platform_for_current_buildfile
 do_not_use_repo_cfg = shim.do_not_use_repo_cfg
-rpm_vset = shim.rpm_vset
 repository_name = shim.repository_name
 target_utils = shim.target_utils
 alias = shim.alias
@@ -275,4 +272,3 @@ third_party = struct(
     source = shim.third_party.source,
     libraries = _third_party_libraries,
 )
-thrift_library = shim.thrift_library