[wasm] Remove unnecessary linker flag from lit config

Author: kateinoigakukun

test/lit.cfg

@@ -1850,7 +1850,6 @@ elif run_os == 'wasi':
     config.target_build_swift = ' '.join([
         config.swiftc,
         '-target', config.variant_triple,
-        '-Xclang-linker', '--sysroot=%s' % config.variant_sdk,
         '-sdk', config.variant_sdk,
         '-toolchain-stdlib-rpath', config.resource_dir_opt, 
         mcp_opt, config.swift_test_options,