Parser: Remove markNoConversion for displaytitle error message

Parser: Remove markNoConversion for displaytitle error message

bacd87e49 moved the displaytitle error message from the content to
outside of the content. Only the content is converted by the language
conversion. The error message outside of the content is not converted.
Therefor markNoConversion is not needed here anymore.

This change removes the -{R|...}- around the displaytitle in the error
message when the language converter is active.

Bug: T208249
Change-Id: Ieec43e9af045d19b0b7a82afb889e076b347eed1