tests/cmdline/cmd_showbc: Fix test now that 1 value is stored on stack.

This corresponds to the change in the way exception values are stored on
the Python value stack.

tests/cmdline/cmd_showbc.py.exp

@@ -242,8 +242,6 @@ arg names:
 \\d\+ POP_BLOCK
 \\d\+ JUMP \\d\+
 \\d\+ POP_TOP
-\\d\+ POP_TOP
-\\d\+ POP_TOP
 \\d\+ LOAD_DEREF 14
 \\d\+ POP_TOP
 \\d\+ POP_EXCEPT