library: do not include dhm.c in the build

The file was cancelled from the tf-psa-crypto repo following the removal
of MBEDTLS_DHM_C.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/Makefile b/library/Makefile
index b874acf..61b2623 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -139,7 +139,6 @@
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/constant_time.o \
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/ctr_drbg.o \
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/des.o \
-	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/dhm.o \
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/ecdh.o \
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/ecdsa.o \
 	     $(TF_PSA_CRYPTO_DRIVERS_BUILTIN_SRC_PATH)/ecjpake.o \