fix: dynamic if teardown

[BeksOmega]

Dependent on #1885

Work on #1843

Tears down the entire block instead of leaving the top input. This was causing a bug as outlined below.

Also deprecated minInputs since it's not being used, and implementing it like I did for the list blocks seems like more hastle than it's worth.

The Bug

Sometimes your if an else-ifs would be out of order, or you would get two else-ifs instead of one if and one else-if. This only happened when loading from the old serialization format.

To Reproduce

1. Open up the dynamic connections plugin on the block-dynamic-serialization branch.
2. Load the following XML into the demo:

<xml xmlns="https://developers.google.com/blockly/xml">
  <block type="controls_if" id="sakn]=Bg/(7J)B4fgb%_" x="249" y="279">
    <mutation inputs="1,2" else="false" next="3"></mutation>
    <value name="IF1">
      <block type="logic_boolean" id="B5(rV1:^?a_:eoCGcNCN">
        <field name="BOOL">TRUE</field>
      </block>
    </value>
    <value name="IF2">
      <block type="logic_boolean" id="a`lufX}(^;Q)EbJYSdc@">
        <field name="BOOL">FALSE</field>
      </block>
    </value>
  </block>
</xml>

3. Drag the block.
4. Observe.
   

Testing

Retested the reproduction steps and this no longer reproduces.