Revert "[Diagnostic] Add ftabstop to -Wmisleading-indentation"

This reverts commit b47b35ff.

This caused failed asserts (Assertion `FIDAndOffset.second >
ColNo && "Column number smaller than file offset?"' failed.)
on a source file with a single line containing
"int main (void) { for( int i = 0; i < 9; i++ ); return 0; }".