[Bug-apl] Tab completion doesn't track )ERASE

[David B. Lamkins]

Tab completion doesn't know that a symbol has been removed.

In the following, <Tab> is the tab character.

      ⎕fx 'foo'
foo
      f<Tab>
      ⎕ex 'foo'
1
      ⎕nc 'foo'
0
      f<Tab>
VALUE ERROR
      foo
      ^