[minor] Change expression evaluation cli argument to -Xexpression

compiler/testData/cli/jvm/extraHelp.out

@@ -18,6 +18,7 @@ where advanced options include:
                              'enable' since language version 1.3
   -Xdump-declarations-to=<path> Path to JSON file to dump Java to Kotlin declaration mappings
   -Xdisable-standard-script  Disable standard kotlin script support
+  -Xexpression               Evaluate the given string as a Kotlin script
   -Xfriend-paths=<path>      Paths to output directories for friend modules (whose internals should be visible)
   -Xmultifile-parts-inherit  Compile multifile classes as a hierarchy of parts and facade
   -Xir-check-local-names     Check that names of local classes and anonymous objects are the same in the IR backend as in the old backend

compiler/testData/cli/jvm/help.out

@@ -2,7 +2,6 @@ Usage: kotlinc-jvm <options> <source files>
 where possible options include:
   -classpath (-cp) <path>    List of directories and JAR/ZIP archives to search for user class files
   -d <directory|jar>         Destination for generated class files
-  -expression                Evaluate the given string as a Kotlin script
   -include-runtime           Include Kotlin runtime into the resulting JAR
   -java-parameters           Generate metadata for Java 1.8 reflection on method parameters
   -jdk-home <path>           Include a custom JDK from the specified location into the classpath instead of the default JAVA_HOME