Enable coverage for simplicity/secp256k1

While the bitcoin/elements project testing isn't trying to gain coverage of the regular
libsecp256k1 library, in our case we do want our (fuzz) testing to cover
simplicity's own copy of libsecp256k1, which has been specifically trimmed down
to only include functionality needed by simplicity's jets.

Author: roconnor-blockstream

Makefile.am

@@ -195,7 +195,6 @@ LCOV_FILTER_PATTERN = \
 	-p "src/crypto/ctaes" \
 	-p "src/minisketch" \
 	-p "src/secp256k1" \
-	-p "src/simplicity/secp256k1" \
 	-p "depends"
 
 DIR_FUZZ_SEED_CORPUS ?= qa-assets/fuzz_seed_corpus