Removed reference to $(srcdir) in test/load/Makefile.am

For some reason it causes the following error

```
10:58:19 Makefile:598: ../../libpromises/.deps/lastseen.Po: No such file or directory
10:58:19 make[3]: *** No rule to make target '../../libpromises/.deps/lastseen.Po'.  Stop.
```

in bootstrap_pr while doing `make dist` in Jenkins.

Ticket: CFE-2780
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

tests/load/Makefile.am

@@ -54,8 +54,8 @@ db_load_LDADD = ../unit/libdb.la
 
 
 lastseen_load_SOURCES = lastseen_load.c \
-	$(srcdir)/../../libpromises/lastseen.c \
-	$(srcdir)/../../libntech/libutils/statistics.c
+	../../libpromises/lastseen.c \
+	../../libntech/libutils/statistics.c
 lastseen_load_LDADD = ../unit/libdb.la ../../libpromises/libpromises.la
 endif