bugfix: revert pydantic dependency introduction

[fselmo]

What was wrong?

• The introduction of pydantic as a dependency in 0.11.x was not necessary and it was not appropriate for a patch release (see issue ethereum/eth-account#270). This is simple enough to remove for 0.11.x and leave it for 0.12.x.

Related to Issue #270

How was it fixed?

• Revert the use of pydantic as a dependency. This is simple enough to handle by defining __init__() methods that validate inputs to the data coming into each of the blob class objects.

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Note: By removing pydantic, we don't validate the input's type in the data models but this should be consistent with the rest of the library up to 0.11.0. That's one additional benefit we get from the pydantic implementation in 0.12.x.

Todo:

• [x] Clean up commit history
• [x] Add entry to the release notes

Cute Animal Picture

[fselmo]

bugfix and removal newsfragments to explain the patch as a removal of pydantic dependency for 0.11.x?

[kclowes]

bugfix and removal newsfragments to explain the patch as a removal of pydantic dependency for 0.11.x?

I think bugfix might suffice, but I'll leave it up to your good judgement :)