Just:
rm $(ls -I "*.txt" ) #Deletes file type except *.txt
Or:
rm $(ls -I "*.txt" -I "*.pdf" ) #Deletes file types except *.txt & *.pdf
Just:
rm $(ls -I "*.txt" ) #Deletes file type except *.txt
Or:
rm $(ls -I "*.txt" -I "*.pdf" ) #Deletes file types except *.txt & *.pdf