pem.c: remove redundant compilation guard

If MBEDTLS_MD5_C is not defined MBEDTLS_USE_PSA_CRYPTO must be defined due to PEM_RFC1421.

*** Comparing before-default -> after-default ***
   x509parse: total 723; skipped  26 ->  26
   x509write: total  41; skipped   8 ->   8
         pem: total  13; skipped   0 ->   0
         oid: total  28; skipped   0 ->   0

*** Comparing before-full -> after-full ***
   x509parse: total 723; skipped  25 ->  25
   x509write: total  41; skipped   0 ->   0
         pem: total  13; skipped   0 ->   0
         oid: total  28; skipped   0 ->   0

*** Comparing reference -> drivers ***
   x509parse: total 723; skipped  89 ->  89
   x509write: total  41; skipped   3 ->   3
         pem: total  13; skipped   0 ->   0
         oid: total  28; skipped   0 ->   0

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/library/pem.c b/library/pem.c
index 5e8f268..ca41cf0 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -143,7 +143,6 @@
     return( ret );
 }
 #else
-#if defined(MBEDTLS_USE_PSA_CRYPTO)
 static int pem_pbkdf1( unsigned char *key, size_t keylen,
                        unsigned char *iv,
                        const unsigned char *pwd, size_t pwdlen )
@@ -254,8 +253,7 @@
 
     return( ret );
 }
-#endif
-#endif
+#endif /* MBEDTLS_MD5_C */
 
 #if defined(MBEDTLS_DES_C)
 /*