Revert "i965: Switch to scalar TCS by default."

This reverts commit b593737e.

Apparently it causes GPU hangs on some image load store tests.
Let's turn it back off until we figure out why.

src/mesa/drivers/dri/i965/brw_compiler.c

@@ -153,7 +153,7 @@ brw_compiler_create(void *mem_ctx, const struct brw_device_info *devinfo)
    compiler->scalar_stage[MESA_SHADER_VERTEX] =
       devinfo->gen >= 8 && !(INTEL_DEBUG & DEBUG_VEC4VS);
    compiler->scalar_stage[MESA_SHADER_TESS_CTRL] =
-      devinfo->gen >= 8 && env_var_as_boolean("INTEL_SCALAR_TCS", true);
+      devinfo->gen >= 8 && env_var_as_boolean("INTEL_SCALAR_TCS", false);
    compiler->scalar_stage[MESA_SHADER_TESS_EVAL] =
       devinfo->gen >= 8 && env_var_as_boolean("INTEL_SCALAR_TES", true);
    compiler->scalar_stage[MESA_SHADER_GEOMETRY] =