Jelly, 6 bytes
s2Q€Ṗ€
How it works
s2Q€Ṗ€ Main link. Argument: S (string)
s2 Split the string into pairs of characters.
Q€ Deduplicate each pair.
This removes the second character iff it is equal to the first.
Ṗ€ Pop each; remove the last character of each pair/singleton.