Don't output "exec() finished with..." error message

It's useless because the result of the compiler is always evident (it outputs
either diagnostics or an exception stack trace)

compiler/integration-tests/testData/compilationFailed/hello.compile.expected

@@ -1,6 +1,5 @@
 
 ERR:
 ERROR: [TestData]/hello.kt: (4, 5) Unresolved reference: a
-exec() finished with COMPILATION_ERROR return code
 
 Return code: 1

compiler/integration-tests/testData/syntaxErrors/test.compile.expected

@@ -1,6 +1,5 @@
 
 ERR:
 ERROR: [TestData]/test.kt: (4, 20) Expecting an element
-exec() finished with COMPILATION_ERROR return code
 
 Return code: 1