A few remaining cases in Context.cpp are actually
implemented, so we can remove the UNIMPLEMENTED()
calls in these cases: Primitive restart, uniform
blocks, fragment inputs and vertex outputs are all
implemented. Also, the implementation can legally
support 0 program binary formats.

Change-Id: I74b51b511c66170e284ac5d82f573453332872cc
Reviewed-on: https://swiftshader-review.googlesource.com/8788Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>