sed, 28 bytes

:
s#(+)\|\[:\]\|{|}\|<->##
t

sed doesn't have a concept of truthy/falsy, so I'm considering an empty string truthy and a non-empty string falsy. This checks out if we consider the conditional /^$/.

Try it online!

sed, 28 27 bytes

:
s#(+)\|\[:]\|{|}\|<->##
t

sed doesn't have a concept of truthy/falsy, so I'm considering an empty string truthy and a non-empty string falsy. This checks out if we consider the conditional /^$/.

Thanks to @Neil for golfing off 1 byte!

Try it online!