Python: Fix bad join in `py/redundant-assignment`
Python: Fix bad join in `py/redundant-assignment`

A minor thing, but still best avoided:
```
Tuple counts for RedundantAssignment::pyflakes_commented_line#bb/2@0477c7 after 14.2s:
160826   ~0%     {2} r1 = SCAN py_comments OUTPUT In.2, In.1
160826   ~0%     {3} r2 = JOIN r1 WITH project#Files::Location::hasLocationInfo_dispred#bfffff ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Rhs.2 'result'
160826   ~3%     {3} r3 = JOIN r2 WITH files_10#join_rhs ON FIRST 1 OUTPUT Lhs.2 'result', Lhs.1, Rhs.1 'file'
46672419 ~4%     {4} r4 = JOIN r3 WITH Files::Location::getStartLine_dispred#bf_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.2 'file', Lhs.1, Lhs.0 'result'
3951     ~0%     {4} r5 = JOIN r4 WITH Files::Location::getFile_dispred#bf ON FIRST 2 OUTPUT Lhs.2, Lhs.3 'result', Lhs.1 'file', toLower(Lhs.2)
0        ~0%     {4} r6 = SELECT r5 ON In.3 contains "pyflakes"
0        ~0%     {2} r7 = SCAN r6 OUTPUT In.2 'file', In.1 'result'
                return r7
```

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