cancel requirements for astropy etc.

.readthedocs-requirements.txt

 sphinx>=4.2.0
-astropy>=5.0.1
-numpy>=1.20.3
-scipy>=1.7.1
-matplotlib>=3.4.3
+#astropy>=5.0.1
+#numpy>=1.20.3
+#scipy>=1.7.1
+#matplotlib>=3.4.3