exchange: replace a "not x in ys" by more Pythonic "x not in ys"
Found by one of our (Google-)internal tools.
Differential Revision: https://phab.mercurial-scm.org/D7546
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2