fix: prune unused getDecimals

Author: QGarchery

src/interfaces/IERC4626.sol

@@ -3,5 +3,4 @@ pragma solidity ^0.8.0;
 
 interface IERC4626 {
     function convertToAssets(uint256) external view returns (uint256);
-    function decimals() external view returns (uint256);
 }

src/libraries/VaultLib.sol

@@ -15,12 +15,4 @@ library VaultLib {
 
         return vault.convertToAssets(shares);
     }
-
-    /// @dev Returns the number of decimals of a `vault`, seen as an ERC20.
-    /// @dev When `vault` is the address zero, returns 0.
-    function getDecimals(IERC4626 vault) internal view returns (uint256) {
-        if (address(vault) == address(0)) return 0;
-
-        return vault.decimals();
-    }
 }