Remove mbedtls/build_info from pkcs7.c

This commit removes #include "mbedtls/buildinfo.h" from pkcs7.c as it is
not needed unlike other C modules.

Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
diff --git a/library/pkcs7.c b/library/pkcs7.c
index 9b53cee..ff0567c 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -4,7 +4,6 @@
  */
 #include "x509_internal.h"
 
-#include "mbedtls/build_info.h"
 #if defined(MBEDTLS_PKCS7_C)
 #include "mbedtls/pkcs7.h"
 #include "mbedtls/asn1.h"