README.md: Drop trailing spaces and "Git submodule"

:Release Notes:
We're not using git submodules for some time.

:Detailed Notes:

:Testing Performed:
N/A

:QA Notes:
N/A

:Issues Addressed:
N/A

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: Ia069e29e79aa81ac1def18aa8aee89edb76ca354
Reviewed-on: https://g2g.palm.com/6168
Reviewed-by: DCO Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>