This can be done with the Find and Replace command, which you can open with CTRL+H.
In the find field enter "^g" (a caret or circumflex, followed immediately by g without the quotes) and in the replace field enter nothing, since you're trying to remove the graphics. The carat G represents any graphic (image) in the document.
Hit ALT+A to activate the Replace All button and this should have removed all images in the file, leaving only text. Then activate the close button on the Find and Replace dialog.
Brian - Windows 10 Home, 64-Bit, Version 1703, Build 15063 (dot level on request - it changes too often to keep in signature)