runtime: consider removing randomizedheapbase64 GOEXPERIMENT opt-out

[rolandshoemaker]

As far as I'm aware we haven't hit any particular issues with the randomizedheapbase64 GOEXPERIMENT, which has been enabled by default since 1.26. It does make some debugging tools behave a little funky, but I believe most have figured out ways around it.

We should consider removing the GOEXPERIMENT, which at this point exists solely to let users opt-out of this behavior.

[prattmic]

cc @golang/runtime

[rolandshoemaker]

For reference, telemetry does show relatively high usage of the norandomizeheapbase64 GOEXPERIMENT: https://telemetry.go.dev/#charts%3acmd%2fgo%3ago%2fgoexperiment.