Move some typedefs to base.h.

Change-Id: I48bcf3a989752901903d68b50665910b9372a2ff
Reviewed-on: https://boringssl-review.googlesource.com/8860
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
diff --git a/include/openssl/dsa.h b/include/openssl/dsa.h
index 2a621da..24cfcde 100644
--- a/include/openssl/dsa.h
+++ b/include/openssl/dsa.h
@@ -129,9 +129,9 @@
 /* Signatures. */
 
 /* DSA_SIG_st (aka |DSA_SIG|) contains a DSA signature as a pair of integers. */
-typedef struct DSA_SIG_st {
+struct DSA_SIG_st {
   BIGNUM *r, *s;
-} DSA_SIG;
+};
 
 /* DSA_SIG_new returns a freshly allocated, DIG_SIG structure or NULL on error.
  * Both |r| and |s| in the signature will be NULL. */