Remove mpmath dependency pin (#2640)

Summary:
`mpmath` was pinned in 02e8014 due to an issue with a sympy alpha release. This should not be necessary anymore.

Also re-ordered the dependency list to group deps together.

Pull Request resolved: #2640

Reviewed By: saitcakmak

Differential Revision: D66580632

Pulled By: Balandat

fbshipit-source-id: 5b3e45316021be810f7470dcd4753c11495efa48

requirements.txt

@@ -1,9 +1,8 @@
-multipledispatch
-scipy
-mpmath>=0.19,<=1.3
-torch>=2.0.1
-pyro-ppl>=1.8.4
 typing_extensions
 pyre_extensions
 gpytorch==1.13
 linear_operator==0.5.3
+torch>=2.0.1
+pyro-ppl>=1.8.4
+scipy
+multipledispatch