deps: unpin biopython, pin bcbio-gff to 0.7*

Biopython was fixed to <=1.80 in #1152
because bcbio-gff <=0.6.9 requires deprecated Biopython functionality that was removed in 1.81

A fix to bcbio-gff was released as 0.7.0, see chapmanb/bcbb#137 chapmanb/bcbb#136
So now we can pin bcbio-gff to >=0.7.0 and remove the pin
of Biopython

Note added in #1170 can hence be removed

setup.py

@@ -51,12 +51,8 @@
     package_data = {'augur': ['data/*']},
     python_requires = '>={}'.format('.'.join(str(n) for n in py_min_version)),
     install_requires = [
-        "bcbio-gff >=0.6.0, ==0.6.*",
-        # TODO: Remove biopython <=1.80 pin when 1.81/higher is supported by a
-        # new version of bcbio-gff¹ and that is also pinned, or when bcbio-gff
-        # is no longer a dependency.
-        # ¹ https://github.com/chapmanb/bcbb/issues/136
-        "biopython >=1.67, !=1.77, !=1.78, <=1.80",
+        "bcbio-gff >=0.7.0, ==0.7.*",
+        "biopython >=1.67, !=1.77, !=1.78",
         "cvxopt >=1.1.9, ==1.*",
         "isodate ==0.6.*",
         "jsonschema >=3.0.0, ==3.*",