Prepare for TypeScript 3.7

Summary:
These are the only four errors currently happening when upgrading to the 3.7 beta.
Luckily, these are all forwards-compatible changes.

Reviewed By: jknoxville

Differential Revision: D17711797

fbshipit-source-id: 429036e90300c81848cc3252b67bb89871ff2e32

src/plugins/cpu/index.tsx

@@ -391,9 +391,9 @@ export default class CPUFrequencyTable extends FlipperDevicePlugin<
     });
   };
 
-  teardown = () => {
+  teardown() {
     this.cleanup();
-  };
+  }
 
   buildRow = (freq: CPUFrequency, idx: number) => {
     const selected = this.state.selectedIds.indexOf(idx) >= 0;