Debugger cdb: Fix dump of unsigned __int64 for cdb 6.11

The local variable output of unsigned __int64 differ between 6.11
and 6.2

6.11: 0x222`23456789
6.2:  0x00000222`23456789

So we must iterate over the value to find and remove the 64bit separator
(`) instead of just expect it at the 10th character.

Change-Id: I8017c83707b29fa0a510bf621e57e9da6895b63a
Reviewed-by: hjk <hjk121@nokiamail.com>