Lose mention of COMPOSE phaser

Associated with rakudo/rakudo#5193

Note: there are *NO* tests for the COMPOSE phaser

Author: lizmat

doc/Language/phasers.pod6

@@ -48,7 +48,6 @@ CONTROL {...} #  catch control exceptions, before LEAVE
    LAST {...} #  supply tapped by whenever-block is done, runs very last
    QUIT {...} #  catch async exceptions within a whenever-block, runs very last
 
-COMPOSE {...} #  when a role is composed into a class (Not yet implemented)
   CLOSE {...} #  appears in a supply block, called when the supply is closed
 =end code
 
@@ -130,7 +129,6 @@ Compilation begins
 =for code :skip-test<listing>
       BEGIN {...} #  at compile time, As soon as possible, only ever runs once
       CHECK {...} #  at compile time, As late as possible, only ever runs once
-    COMPOSE {...} #  when a role is composed into a class (Not yet implemented)
 
 Execution begins
 
@@ -417,12 +415,6 @@ C<take>, C<warn>, C<proceed> and C<succeed>.
     # 0
 
 
-=head1 Object phasers
-
-=head2 X<COMPOSE|Phasers,COMPOSE> (Not yet implemented)
-
-Runs when a role is composed into a class.
-
 =head1 Asynchronous phasers
 
 =head2 X<LAST|Asynchronous phasers,LAST>