Stop describing the raw IllegalAccessError on the Gradle page

openjavaformat/open-java-format#79 makes formatDiff stop before the
first file when the Gradle JVM does not export javac's packages, with a
message that names the two settings, so the sentence that described the
raw IllegalAccessError and the module it mentioned no longer matches.
The page now says to pick one of the two settings and what happens
without either.

Author: abashev

docs/get-started/gradle.md

@@ -35,9 +35,8 @@ The formatter itself is downloaded from Maven Central, in the same version as th
 
 ## Choose how the formatter runs
 
-The formatter reads javac's internal classes, which a plain Gradle JVM does not open up. Without one
-of the two settings below, `formatDiff` fails with an `IllegalAccessError` that mentions
-`module jdk.compiler does not export com.sun.tools.javac.parser`.
+The formatter reads javac's internal classes, which a plain Gradle JVM does not open up. Pick one of
+the two settings below; without either, `formatDiff` stops before the first file and names them.
 
 === "Native binary"