Remove unused function prototype.

This function was removed in
https://boringssl-review.googlesource.com/c/boringssl/+/33065.

Change-Id: Ib8adefeabafa58e22e1b0fdd406f73c234c2e5e7
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/40524
Reviewed-by: Adam Langley <agl@google.com>

crypto/fipsmodule/ec/internal.h

diff --git a/crypto/fipsmodule/ec/internal.h b/crypto/fipsmodule/ec/internal.h
index d8f0a0b..4ce31c9 100644
--- a/crypto/fipsmodule/ec/internal.h
+++ b/crypto/fipsmodule/ec/internal.h
@@ -378,10 +378,6 @@
                                          uint8_t *out_y, size_t *out_len,
                                          size_t max_out, const EC_RAW_POINT *p);
 
-// ec_field_element_to_scalar reduces |r| modulo |group->order|. |r| must
-// previously have been reduced modulo |group->field|.
-int ec_field_element_to_scalar(const EC_GROUP *group, BIGNUM *r);
-
 void ec_GFp_mont_mul(const EC_GROUP *group, EC_RAW_POINT *r,
                      const EC_RAW_POINT *p, const EC_SCALAR *scalar);
 void ec_GFp_mont_mul_base(const EC_GROUP *group, EC_RAW_POINT *r,