It seems like SwiftShader already supports surfaceless contexts properly in
eglMakeCurrent, so we might as well expose the extension strings.

Change-Id: I3c1b85296c46536df9a8bd754856d825307181d0
Reviewed-on: https://swiftshader-review.googlesource.com/17948Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>