Revert "Make aToken.initialize public and virtual so it can be extended"

This reverts commit 8865203.

contracts/protocol/tokenization/AToken.sol

@@ -59,7 +59,7 @@ contract AToken is VersionedInitializable, ScaledBalanceTokenBase, EIP712Base, I
     string calldata aTokenName,
     string calldata aTokenSymbol,
     bytes calldata params
-  ) public virtual override initializer {
+  ) external override initializer {
     require(initializingPool == POOL, Errors.POOL_ADDRESSES_DO_NOT_MATCH);
     _setName(aTokenName);
     _setSymbol(aTokenSymbol);