Delete a spreadsheet cell in Google Drive for Android
I am using the latest version of Drive. I know there was a big update not long ago and I see this question was asked before the update. 

Anyway, just go to the cell/column/row and highlight it. Then tap on it again.

Options will come up for "Clear" if it is just a cell or range. If it is a row or column "Delete" will be one of the options. 

I hope this helps.