chore(Identity): remove Identity Hub from EDC

[marcgs]

What this PR changes/adds

Remove IdentityHub code from EDC core as a new implementation is available in a separate repository: https://github.com/eclipse-dataspaceconnector/IdentityHub

Why it does that

Remove unused code from EDC.

Linked Issue(s)

Closes #1373

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• assigned appropriate label? (exclude from changelog with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[codecov-commenter]

Codecov Report

Merging #1816 (874a35b) into main (797b8ff) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1816      +/-   ##
==========================================
- Coverage   67.92%   67.91%   -0.02%     
==========================================
  Files         803      767      -36     
  Lines       17051    16419     -632     
  Branches     1082     1071      -11     
==========================================
- Hits        11582    11151     -431     
+ Misses       4998     4804     -194     
+ Partials      471      464       -7     

Impacted Files	Coverage Δ
...aceconnector/iam/did/IdentityDidCoreExtension.java	0.00% <ø> (-66.67%)	⬇️
...iation/ProviderContractNegotiationManagerImpl.java	90.00% <0.00%> (-0.56%)	⬇️
...ceconnector/iam/did/spi/document/DidConstants.java
...r/iam/did/spi/document/EllipticCurvePublicKey.java
...taspaceconnector/iam/did/spi/document/Service.java
...ector/iam/did/spi/document/VerificationMethod.java
...ctor/iam/did/spi/document/DidDocumentMetadata.java
...aceconnector/iam/did/spi/key/PublicKeyWrapper.java
...ataspaceconnector/iam/did/spi/document/Method.java
... and 2 more

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