Fix error report when active color buffer has no fs output Also modify or remove some tests to sync up with the expected behavior stated in spec. Related to https://github.com/KhronosGroup/WebGL/pull/2780 If any draw buffer with an attachment does not have a defined fragment shader output, draws generate INVALID_OPERATION. Also remove Framebuffer masking for inactive outputs. This workaround is no longer necessary as the WebGL spec has changed. It also was never fully working and had bugs with certain orders of calls. Bug: angleproject:2872 Bug: chromium:927908 Bug: chromium:943538 Change-Id: I73715a6ab851ae3db7096f49ea0a9fdd6f576703 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1530018 Commit-Queue: Shrek Shao <shrekshao@google.com> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>