Simplify benchmark patterns in mypy-strict.ini (pytorch#55700)

Summary:
These two lines were added in pytorch#53296, but they are needlessly complicated; this PR consolidates them.

Pull Request resolved: pytorch#55700

Test Plan:
Run this command, and verify that the same number of files is given both before and after this PR:
```
mypy --config=mypy-strict.ini
```

Reviewed By: robieta

Differential Revision: D27684278

Pulled By: samestep

fbshipit-source-id: a34968cdff29cb8ad83813b277114224b5e37569

mypy-strict.ini

@@ -36,8 +36,7 @@ strict_equality = True
 
 files =
     .github/scripts/generate_binary_build_matrix.py,
-    benchmarks/instruction_counts/*.py,
-    benchmarks/instruction_counts/*/*.py,
+    benchmarks/instruction_counts,
     tools/autograd/*.py,
     tools/clang_tidy.py,
     tools/codegen/*.py,