It does remove the if, but it keeps the constant to maintain the behaviour.

>perl -MO=Concise,-exec,f -e"sub f { return 1 if 0 }"
main::f:
1  <;> nextstate(main 1 -e:1) v
2  <$> const[IV 0] s/SHORT
3  <1> leavesub[1 ref] K/REFC,1
-e syntax OK
[download]

Compared to:

>perl -MO=Concise,-exec,f -e"sub f { return 1 if $c }"
main::f:
1  <;> nextstate(main 1 -e:1) v
2  <#> gvsv[*c] s
3  <|> and(other->4) K/1
4      <0> pushmark s
5      <$> const[IV 1] s
6      <@> return K
7  <1> leavesub[1 ref] K/REFC,1
-e syntax OK
[download]

Note the and operator (used to implement if) is missing from the first snippet.