Revert "Add gyp build of sel_ldr and irt_core for ARM."

Revert "Add gyp build of sel_ldr and irt_core for ARM."

This reverts commit r12589 since it introduces a dependency
on the linux ARM cross compiler when to to gyp build
and this is not yet installed on the chromium trybots.
This change should be re-applied once this compiler is
installed: http://crbug.com/335303

> Add gyp build of sel_ldr and irt_core for ARM.
>
> The irt core can be built on all platforms but sel_ldr
> can only be built on linux (the only platform with an
> arm cross compiler).
>
> BUG=266959
> R=jvoung@chromium.org
>
> Review URL: https://codereview.chromium.org/93513013

BUG=266959
R=jvoung@chromium.org

Committed: https://src.chromium.org/viewvc/native_client?view=rev&revision=12639

[jvoung (off chromium), 2014-01-18 00:53:13]

lgtm

[Sam Clegg, 2014-01-18 01:56:42]

Committed patchset #1 manually as r12639 (presubmit successful).