Remove indenting APIs from Logger. These are thread unsafe by design.

Loggers are not owned by a specific thread and many are used by multiple threads. The indenting APIs could not be made to be thread safe in any way as they exist, so they have been removed. The data races caused by the indenting APIs are actually an important stability issue that could cause the indentation level to go out of bounds and crash the product.

If you were using the indentation APIs, you will need to rewrite the usage to manually manage the indentation level in a thread safe way.