Do not force benchmarks to be statically linked.

Libtool will do the right thing and use whatever is available
 based on --enable-shared/--enable-static.

This also means that some of the things we build actually
 test the dynamic library.

src/modules/ecdh/Makefile.am.include

@@ -5,5 +5,4 @@ if USE_BENCHMARK
 noinst_PROGRAMS += bench_ecdh
 bench_ecdh_SOURCES = src/bench_ecdh.c
 bench_ecdh_LDADD = libsecp256k1.la $(SECP_LIBS)
-bench_ecdh_LDFLAGS = -static
 endif

src/modules/recovery/Makefile.am.include

@@ -5,5 +5,4 @@ if USE_BENCHMARK
 noinst_PROGRAMS += bench_recover
 bench_recover_SOURCES = src/bench_recover.c
 bench_recover_LDADD = libsecp256k1.la $(SECP_LIBS)
-bench_recover_LDFLAGS = -static
 endif

src/modules/schnorr/Makefile.am.include

@@ -7,5 +7,4 @@ if USE_BENCHMARK
 noinst_PROGRAMS += bench_schnorr_verify
 bench_schnorr_verify_SOURCES = src/bench_schnorr_verify.c
 bench_schnorr_verify_LDADD = libsecp256k1.la $(SECP_LIBS)
-bench_schnorr_verify_LDFLAGS = -static
 endif