[chore] Revert @sigma table factor

[ayman-sigma]

I'm was trying to update our local clone to the upstream version. These changes are not needed anymore and might cause unnecessary conflicts.

[coveralls]

Pull Request Test Coverage Report for Build 11905222784

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 26 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.07%) to 89.041%

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Files with Coverage Reduction	New Missed Lines	%
src/ast/query.rs	2	85.37%
src/parser/mod.rs	2	93.17%
tests/sqlparser_common.rs	3	89.46%
src/lib.rs	19	12.2%

Totals
Change from base Build 9932379092:	-0.07%
Covered Lines:	26746
Relevant Lines:	30038

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💛 - Coveralls

[ayman-sigma]

Closing this in favor to #29. I just realized I should have just made the merge here.