Remove obsolete reference to _ret in migration guide

Signed-off-by: Dave Rodgman <[email protected]>

docs/3.0-migration-guide.md

@@ -240,7 +240,7 @@ relevant as the countermeasure is now always on at no cost in code size.
 
 ### SHA-512 and SHA-256 output type change
 
-The output parameter of `mbedtls_sha256_finish_ret()`, `mbedtls_sha256_ret()`, `mbedtls_sha512_finish_ret()`, `mbedtls_sha512_ret()` now has a pointer type rather than array type. This makes no difference in terms of C semantics, but removes spurious warnings in some compilers when outputting a SHA-384 hash into a 48-byte buffer or a SHA-224 hash into a 28-byte buffer.
+The output parameter of `mbedtls_sha256_finish()`, `mbedtls_sha256()`, `mbedtls_sha512_finish()`, `mbedtls_sha512()` now has a pointer type rather than array type. This makes no difference in terms of C semantics, but removes spurious warnings in some compilers when outputting a SHA-384 hash into a 48-byte buffer or a SHA-224 hash into a 28-byte buffer.
 
 This makes no difference to a vast majority of applications. If your code takes a pointer to one of these functions, you may need to change the type of the pointer.