Delete `fgArgInfo::ArgsComplete():hasStackArgs` local var. (#27350)
Delete `fgArgInfo::ArgsComplete():hasStackArgs` local var. (#27350)

`fgArgInfo` has a field with the same name and the same function. The duplication happened because the local var was added in 2011 and the struct field was added in 2014.

PVS warning:  The 'hasStackArgs' local variable possesses the same name as one of the class members, which can result in a confusion. morph.cpp 1247
poizan42/coreclr,poizan42/coreclr,poizan42/coreclr,poizan42/coreclr,cshung/coreclr,cshung/coreclr,poizan42/coreclr,cshung/coreclr,cshung/coreclr,cshung/coreclr,cshung/coreclr,poizan42/coreclr