biology/peak-classifier: Clean up USES=python

- Fix d6b521a455
- Reapply 1d86601d32

USES=python means USES=python:3.8+ now.

Approved by:	portmgr (blanket)
With hat:	python

biology/peak-classifier/Makefile

@@ -15,7 +15,7 @@ LIB_DEPENDS=	libxtend.so:devel/libxtend libbiolibc.so:biology/biolibc
 RUN_DEPENDS=	bedtools:biology/bedtools \
 		${PYTHON_PKGNAMEPREFIX}matplotlib>0:math/py-matplotlib@${PY_FLAVOR}
 
-USES=		localbase python:3.7+ shebangfix
+USES=		localbase python shebangfix
 USE_GITHUB=	yes
 GH_ACCOUNT=	auerlab