Remove _ Prefix for datatypes from SymCrypt

There are places in the code where the _ prefix is used. I think the only reason that exists is because of historical quirks about how you used to have to use typedef struct in C. The non-underscore version is preferred, so if you have time it would be nice to clean the other occurrences up in a future PR, that would be nice.
`_SYMCRYPT_NUMBER_FORMAT_SYMCRYPT_NUMBER_FORMAT_MSB_FIRST
Ex: `