The script that loads the entry point loaded
glRenderbufferStorageMultisampleEXT from
GL_EXT_multisampled_render_to_texture wrong.  This is fixed in
https://github.com/KhronosGroup/VK-GL-CTS/pull/221.

Bug: angleproject:4836
Change-Id: I843b359b12a042f08a63ba6723cf31bdb8509661
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2331740Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>