Unable to delete an unused partition

Your best bet is to backup / clone the the HD to an external Disk.

Reformat the internal HD which erase ALL data including the orphan partition.

Select one partition form the drop down, GUID partition table and Extended Journaled.

Clone back your Macintosh HD to the internal drive.

https://bombich.com/

You can try reverting your Macintosh HD volume back to a Physical Volume. Right now it's a CoreStorage volume.

Your 2nd screenshot shows that it can be reverted. Towards the bottom you will see Revertible: Yes (no decryption required). Note the Disk name 3 lines above (Disk: disk1). You will need this to revert. Now open Terminal and type: diskutil cs revert disk1 <-- This will revert your CoreStorage volume back to a native file type (Physical volume). Restart your system for the revert to take affect.

Now check to see if you can resize partitions. You might only be able to resize the 2nd partition. If this is so, then to resize both you would need to back up your data then delete the 2nd (Macintosh HD). Then resize the free space back into your 1st one (Untitled) and restore. If you don't want to lose your Macintosh HD, you should be able to boot into it after the revert, open Disk Utility then Edit / Restore and restore your Macintosh HD into your Untitled partition. The Restore command does a block-copy and "clones" the source volume into the destination volume including the Recovery HD. Once this is successful, you will see two Macintosh HD volumes. I would rename the 1st partition's name to something like Macintosh HD1 or something unique then boot into that partition, delete the 2nd partition and resize the free space into your 1st partition.

You can only re-size partitions in the clock-wise directio. It always worked that way. If you can't copy the contents of the second partition to the first one, then delete the second partition, so you can expand the first one clockwise, follow leroydouglas instructions, after moving the current contents to a clone on an external drive.