[baggage] Remove unused private field

[yurishkuro]

There was no way to create a valid property with hasData=false, so the field is not necessary.

[codecov]

Codecov Report

Merging #4318 (e1dd61d) into main (3904523) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4318     +/-   ##
=======================================
- Coverage   78.9%   78.9%   -0.1%     
=======================================
  Files        254     254             
  Lines      20650   20646      -4     
=======================================
- Hits       16307   16303      -4     
  Misses      3998    3998             
  Partials     345     345             

Files Changed	Coverage Δ
baggage/baggage.go	98.9% <100.0%> (-0.1%)	⬇️

[MrAlias]

The following will create a Property with hasData=false:

var p Property

[yurishkuro]

var p Property

which would still be invalid because of empty key, and validity is the only thing hasData field impacts

[MadVikingGod]

I support this change.

We have the hasData to fail fast if the property key is empty. But all property keys require at least one character. This is used ultimately in NewMember. This is thus a CPU optimization for the failure case, but adds memory cost for all cases. If we wanted to keep the same error messages, we could do a length check on the key or check if it is empty.

Note: this doesn't apply to Values that can be empty, so we need some way to check if it has been set.

[pellared]

@MrAlias Can you take another look?