tests: remove `test_` prefix

tests/bitarithm_timings/Makefile

tests/bitarithm_timings/main.c

tests/bloom/Makefile

tests/bloom/generate_sets.py

tests/bloom/main.c

tests/bloom/words.txt.gz

tests/bloom_bytes/Makefile

tests/bloom_bytes/main.c

tests/coap/Makefile

tests/coap/main.c

tests/disable_module/Makefile

tests/disable_module/main.c

tests/float/Makefile

tests/float/README.md

tests/float/main.c

tests/hwtimer/Makefile

tests/hwtimer/main.c

tests/hwtimer/tests/test_hwtimer

tests/hwtimer_spin/Makefile

tests/hwtimer_spin/main.c