Have a look at the Groovy lang API document:
The contains(java.lang.String self, java.lang.String text) method is , Yes, Deprecated. In this sense, IDE is working right. Striking out contains is grammatically correct. Though I find it unnecessary and a bit annoying.
The document says “Use the CharSequence version”. The contains(java.lang.CharSequence self, java.lang.CharSequence text) is not deprecated, will be avaialbe for long term use.
The java.lang.String class implements the java.lang.CharSequence interface. Therefore a Groovy statement:
text.contains("World!")
will stay valid in future.
You can safely ignore it if contains is struck out by IDE.