And then you can just #define assert(...) to eliminate it...oh wait, Go doesn't have a macro-preprocessor.
Go does have build tags, so one could have 2 files for the assert function, each with opposite build tag logic. It does allow for an effective NOP (it would be a stub function and I believe the compiler would eliminate that).
But this would come with a performance penalty: it makes the function you assert() in no longer a leaf function (it calls assert()) and AFAIK, Go only inlines leaf functions. (So, any function in which you call assert() is no longer eligible for inlining.)