Remove SHA-1 as a fallback option

- it's 2020, there shouldn't be too many systems out there where SHA-1 is the
  only available hash option, so its usefulness is limited
- OTOH testing configurations without SHA-2 reveal bugs that are not easy to
  fix in a fully compatible way

So overall, the benefit/cost ratio is not good enough to justify keeping SHA-1
as a fallback option here.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 473488c..255cef3 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -129,9 +129,8 @@
     defined(MBEDTLS_HMAC_DRBG_C) ||         \
     defined(MBEDTLS_SHA512_C) ||            \
     defined(MBEDTLS_SHA256_C) ||            \
-    defined(MBEDTLS_SHA1_C) ||              \
     defined(MBEDTLS_ECP_NO_INTERNAL_RNG))
-#error "MBEDTLS_ECP_C requires a DRBG or SHA module unless MBEDTLS_ECP_NO_INTERNAL_RNG is defined or an alternative implementation is used"
+#error "MBEDTLS_ECP_C requires a DRBG or SHA-2 module unless MBEDTLS_ECP_NO_INTERNAL_RNG is defined or an alternative implementation is used"
 #endif
 
 #if defined(MBEDTLS_PK_PARSE_C) && !defined(MBEDTLS_ASN1_PARSE_C)