[FIR2IR] Unconditionally disable linkViaSignatures on JVM

It was an experimental compilation mode that we don't need anymore.

KT-64809

compiler/testData/ir/irText/firProblems/IntArrayAsVararg.kt

@@ -2,6 +2,9 @@
 // WITH_STDLIB
 // ISSUE: KT-60312
 
+// SEPARATE_SIGNATURE_DUMP_FOR_K2
+// ^ The main function has a different mangled name when it's computed from its K1 descriptor in K/JVM.
+
 fun main() {
     consumeVarargs(1, 2)
     consumeVarargs(arr = intArrayOf(41, 42))