This wasn't a right decision in the first place, the feature flag was
broken in the last rustfmt release, and syntax highlighting of imports
is more important anyway
We simply remove all the CUSTOM_MARKERS before attempting to parse the file.
This allows for the syntax selection to work with most of the test strings.
This allows us to select a string or portions of it and try parsing it as rust
syntax. This is mostly helpful when developing tests where the test
itself contains some rust syntax as a string.
