fix: remove aggregation bits from seen attestation cache

[nflaig]

Motivation

As noted by @twoeths in #7260 (comment), the cache is used for whole committee and not just a single validator which means the cached aggregationBits would be incorrect if reused for another attestation from a different validator.

Description

Remove aggregation bits from seen attestation cache

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.

Project coverage is 48.42%. Comparing base (cfe6c89) to head (71652ea).
Report is 3 commits behind head on devnet-5.

Additional details and impacted files

@@             Coverage Diff              @@
##           devnet-5    #7265      +/-   ##
============================================
- Coverage     48.44%   48.42%   -0.02%     
============================================
  Files           602      602              
  Lines         40321    40332      +11     
  Branches       2057     2056       -1     
============================================
- Hits          19532    19531       -1     
- Misses        20751    20763      +12     
  Partials         38       38              

[twoeths]

lgtm