emsdk

Don't advertise "per_object_debug_info" feature in Bazel. (#969)

It breaks @emsdk in workspaces that have this feature enabled.

The following error appears when using the latest commit:

    cc_toolchain '@emsdk//emscripten_toolchain:everything' with
    identifier 'emscripten-wasm' doesn't define a tool path for 'dwp'

The following error appears after adding `emdwp` tool and scripts:

    output '*.dwo' was not created

Signed-off-by: Piotr Sikora <piotrsikora@google.com>