glslang tear down: Include deleting the keyword map in tear down.  From johnk and sawato shusaku (shusaku.sawato@dmprof.com).

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@31115 e7fa87d3-cd2b-0410-9028-fcbf551c1848