Remove the unreachable partial last block group handling in the EXT4 formatter

[dkovba]

Removes the unreachable partial last block group handling in the EXT4 formatter.

[wlan0]

If the goal is to support a partial final group, the local bitmap change is not the whole story.

The special case adjusts the last group bitmap and its freeBlocksCountLow via blocksInGroup, but later the superblock still derives blocksCount from totalGroups * self.blocksPerGroup and totalFreeBlocks from blocksCount - totalBlocks.

In the used-group path, freeBlocks is computed and then not used. So if this partial-group path ever becomes reachable, the bitmap-level view and the global free-space counters could still differ.