Strip user metadata before codegen passes

[inducer]

Any tags that are not used in code generation should likely be stripped before entering into code generation. Otherwise, we'll get cache misses (and run code generation redundantly) for no good reason.

Likely, this presumptive strip_user_tags should be offered as a "transformation", too. I'm not clear on whether we should leave this to the user or do it automatically, but I'm biased in favor of not doing it automatically.

cc @kaushikcfd @nchristensen