CryptoPkg/BaseCryptLib: remove some duplicate initializations.

clang-analyzer noticed this:

Pk/CryptPkcs7Verify.c:600:5: warning: Value stored to 'OldSize' is never read
    OldSize    = BufferSize;
    ^            ~~~~~~~~~~
Pk/CryptPkcs7Verify.c:644:5: warning: Value stored to 'OldSize' is never read
    OldSize    = BufferSize;
    ^            ~~~~~~~~~~
2 warnings generated.

These are each immediately followed by a loop that initializes them (to
the same values) a second time, and are otherwise only referenced inside
that loop, so there's just no point to these assignments at all.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Long Qin <qin.long@intel.com>

CryptoPkg/Library/BaseCryptLib/Pk/CryptPkcs7Verify.c

@@ -612,7 +612,6 @@ Pkcs7GetCertificatesList (
 
   if (CtxChain != NULL) {
     BufferSize = sizeof (UINT8);
-    OldSize    = BufferSize;
     CertBuf    = NULL;
 
     for (Index = 0; ; Index++) {
@@ -656,7 +655,6 @@ Pkcs7GetCertificatesList (
 
   if (CtxUntrusted != NULL) {
     BufferSize = sizeof (UINT8);
-    OldSize    = BufferSize;
     CertBuf    = NULL;
 
     for (Index = 0; ; Index++) {