BaseTools:Fix GenFds issue for BuildOption replace GenFdsOption

BaseTools:Fix GenFds issue for BuildOption replace GenFdsOption

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=2455

BuildOption is used by TargetTxtClassObj.py
GenFdsOption is used by GenFds.py
When the GenFds tool is used alone (e.g. python3 -m GenFds.GenFds -h)
With the OptionParser function, the first detected function
prints the help message

import TargetTxtClassObj to GenFds,
The BuildOption will be executed and replace GenFdsOption

We removed all objects associated with this problem that
were created directly during the import process
(e.g. BuildOption, BuildTarget = MyOptionParser(),
 TargetTxt = TargetTxtDict())

The Patch is going to fix this issue

Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>