Don't add too many spaces when replacing clauses

[MoonE]

There were unnecessary spaced included in the statement when

• a clause is removed (replaced with empty string)
• the replacement string already has spaces
• the replacement was at the start or end of the statement

This will require some tests to be updated in phpMyAdmin. e. g.: https://github.com/phpmyadmin/phpmyadmin/blob/99c2939eda6c1c3ab9ffe4b1f903bab182d686db/test/classes/Display/ResultsTest.php#L1469

[MauricioFauth]

I think this should target the master branch.