nir/builder_tests: Drop unused lin_ctx.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7323>

src/compiler/nir/tests/builder_tests.cpp

@@ -68,7 +68,6 @@ protected:
    std::vector<nir_intrinsic_instr *> stores;
 
    void *mem_ctx;
-   void *lin_ctx;
 
    nir_builder *b;
 };
@@ -78,7 +77,6 @@ nir_builder_test::nir_builder_test()
    glsl_type_singleton_init_or_ref();
 
    mem_ctx = ralloc_context(NULL);
-   lin_ctx = linear_alloc_parent(mem_ctx, 0);
    static const nir_shader_compiler_options options = { };
    b = rzalloc(mem_ctx, nir_builder);
    *b = nir_builder_init_simple_shader(mem_ctx, MESA_SHADER_COMPUTE, &options);