get rid of outdated logging functions in util::common

[lkuper]

The log_* functions in util::common predate the logging macros and are used in only a handful of places in the compiler. Some aren't being used at all. We should get rid of them and replace the few places they're being used with #debug and #error.

[catamorphism]

A debug_expr macro (for example) would be nice. It's a bit clunky to have to type out #debug("visiting %s", expr_to_str(e)); or whatever all the time. Then debug_expr could be governed by the same logging flags that affect whether #debug and #error macro calls print their results.

[lkuper]

@catamorphism I'm not sure how widely used it would be, considering how little-used these were, but you could always open an issue for #debug_expr