Fixed ahash dependency for wasm

[hzuo]

The WASM special-casing for ahash introduced by #1297 is problematic for a couple of reasons:

1. The compile-time-rng feature is useless without first disabling runtime-rng (which is enabled as a default feature). When both are enabled, runtime-rng takes precendence but we end up bringing in extraneous dependencies for compile-time-rng. It's also misleading to see "compile-time-rng" when in reality it's still runtime-rng.
2. If we really wanted to use compile-time-rng (which we could by setting default-features = false), there's no reason to include getrandom at all since there's no need to get randomness at runtime. But IMO it's a bad default since it leads to non-deterministic / uncacheable builds - see Disable use of const_random! by default rust-lang/hashbrown#155.
3. This broke my use-case since using target_arch also made this config apply to wasm32-unknown-emscripten builds too, even though no special-casing is required for Emscripten. See getrandom's docs on WASM support.

[codecov]

Codecov Report

Base: 83.61% // Head: 83.61% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (544041e) compared to base (ca7f36f).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1407   +/-   ##
=======================================
  Coverage   83.61%   83.61%           
=======================================
  Files         373      373           
  Lines       40288    40288           
=======================================
+ Hits        33685    33686    +1     
+ Misses       6603     6602    -1     

Impacted Files	Coverage Δ
src/bitmap/immutable.rs	86.62% <0.00%> (-0.59%)	⬇️
src/io/ipc/read/file.rs	96.87% <0.00%> (-0.45%)	⬇️
src/offset.rs	85.76% <0.00%> (-0.35%)	⬇️
src/bitmap/utils/slice_iterator.rs	98.78% <0.00%> (+1.21%)	⬆️
src/array/binary/mod.rs	94.08% <0.00%> (+1.47%)	⬆️

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