Delete outdated performance reports, improve a few DDL,DML docs (#4016)

...MatrixOne/Get-Started/Tutorial/NYC-test-with-matrixone.md

...MatrixOne/Get-Started/Tutorial/SSB-test-with-matrixone.md

docs/en/MatrixOne/Overview/NYC Test Performance.md

docs/en/MatrixOne/Overview/SSB Test Performance.md

.../SQL-Reference/Data-Definition-Statements/create-index.md

...ce/SQL-Reference/Data-Definition-Statements/drop-index.md

...e/SQL-Reference/Data-Definition-Statements/primary-key.md

...ence/SQL-Reference/Data-Manipulation-Statements/insert.md

...e/SQL-Reference/Data-Manipulation-Statements/load-data.md

...Statements/operators/cast-functions-and-operators/cast.md

...ence/SQL-Reference/Data-Manipulation-Statements/select.md