Remove unnecessary bit counting code from spark bit_count

[pepijnve]

Which issue does this PR close?

• Followup to bit_count in spark create not fuly compatible with spark #18225 and PR Fix: spark bit_count function #18322

Rationale for this change

Spark's bit_count function always operators on 64-bit values, while the original bit_count implementation in datafusion_spark operated on the native size of the input value.
In order to fix this a custom bit counting implementation was ported over from the Java Spark implementation. This isn't really necessary though. Widening signed integers to i64 and then using i64::count_ones will get you the exact same result and is less obscure.

What changes are included in this PR?

Remove custom bitcount logic and use i64::count_ones instead.

Are these changes tested?

Covered by existing tests that were added for #18225

Are there any user-facing changes?

No

[alamb]

Looks like a nice improvement to me -- thanks @pepijnve

[comphead]

Thanks @pepijnve in Spark/JVM and Rust sometimes there are discrepancies, like treating decimals, regexp, etc.

please add tests for booleans T/F/null