Fix backwards config dependency on oid.c

The file oid.c had conditional inclusion of functions based on a config.h
define that belongs to X.509, which is backwards. For now, just include those
functions unconditionally and rely on the linker to garbage-collect them if
not used.

In the longer term X.509-specific functions are likely to be removed from
libmbedcrypto, but at this step the goal is to preserve the API (and even ABI)
of libmbedcrypto for as long as possible while separating the source trees of
Mbed Crypto and Mbed TLS.
diff --git a/include/mbedtls/oid.h b/include/mbedtls/oid.h
index afe7a81..65e626e 100644
--- a/include/mbedtls/oid.h
+++ b/include/mbedtls/oid.h
@@ -442,7 +442,6 @@
  */
 int mbedtls_oid_get_numeric_string( char *buf, size_t size, const mbedtls_asn1_buf *oid );
 
-#if defined(MBEDTLS_X509_USE_C) || defined(MBEDTLS_X509_CREATE_C)
 /**
  * \brief          Translate an X.509 extension OID into local values
  *
@@ -452,7 +451,6 @@
  * \return         0 if successful, or MBEDTLS_ERR_OID_NOT_FOUND
  */
 int mbedtls_oid_get_x509_ext_type( const mbedtls_asn1_buf *oid, int *ext_type );
-#endif
 
 /**
  * \brief          Translate an X.509 attribute type OID into the short name
diff --git a/library/oid.c b/library/oid.c
index a7ee528..294bbd6 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -148,7 +148,6 @@
     return( MBEDTLS_ERR_OID_NOT_FOUND );                                   \
 }
 
-#if defined(MBEDTLS_X509_USE_C) || defined(MBEDTLS_X509_CREATE_C)
 /*
  * For X520 attribute types
  */
@@ -296,7 +295,6 @@
 
 FN_OID_TYPED_FROM_ASN1(mbedtls_oid_descriptor_t, ext_key_usage, oid_ext_key_usage)
 FN_OID_GET_ATTR1(mbedtls_oid_get_extended_key_usage, mbedtls_oid_descriptor_t, ext_key_usage, const char *, description)
-#endif /* MBEDTLS_X509_USE_C || MBEDTLS_X509_CREATE_C */
 
 #if defined(MBEDTLS_MD_C)
 /*