JVM_IR: make primitive == object slightly less lazy.

Discarding the value used to leave an unused-but-never-destroyed
temporary variable. It's best to not separate calls to `enterTemp`
and `leaveTemp`.

Not sure what kind of test to add though, since this is minor -- if the
result of the comparison is discarded, then the entire statement is more
or less pointless.

 #KT-42251 Fixed

compiler/testData/codegen/bytecodeText/deadCodeElimination/unusedPrimitiveAndObjectEquals.kt

@@ -0,0 +1,12 @@
+var x = 1
+
+fun box() {
+    val y: Number = 1
+    x == y
+}
+
+// 0 equals
+// JVM_TEMPLATES
+// 1 ICMP
+// JVM_IR_TEMPLATES
+// 0 ICMP