Remove support for compiling libANGLE as a dynamic library.

BUG=angle:733

Change-Id: Iacef45b89f234091eb5df505437adabece1e564b
Reviewed-on: https://chromium-review.googlesource.com/232961
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>