ir3: Don't save/restore disasm string pointer

ir3: Don't save/restore disasm string pointer

It's not in the key, so it randomly may or may not be present, and if it
is present then we don't actually save/restore the contents, so we will
save/restore random pointer values from the last run. Turnip already
disables searching the shader cache when assembly is requested, but
still wrote the final ir3_shader_variant which resulted in trying to
save random stale pointers when saving off the executable if a
subsequent compile hit that cache entry.

This fixes flakes in
dEQP-VK.pipeline.pipeline_library.shader_module_identifier.pipeline_from_id.*
for me.

Fixes: 56909868cd1 ("turnip: implement VK_KHR_pipeline_executable_properties")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20056>
(cherry picked from commit 8ba2d612d51497b274ff9c4213e1c373b9bb1ca5)