i965: Remove dead entrypoints to state cache, rename the one that's left.

i965: Remove dead entrypoints to state cache, rename the one that's left.

As we expanded the usage of the state cache, it grew extra
functionality.  However, with the recent state streaming rework, we're
back to the state cache being used only for shader kernels, which is
the piece of GPU state that's actually expensive to compute again from
scratch, since it involves compiling.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>