Do not write version requirements for suspend functions

Previous attempt was at 6807ed6642, but it was reverted in 7771e5914d
(see that commit for the explanation). Now it should be fine to remove
these version requirements.

No issue reported because it's mostly not a user-visible change. The
main effect is that it reduces differences in metadata between K1 and
K2, namely it fixes the ValueClass.kt kotlinp test.

compiler/testData/versionRequirement/nestedClassMembers.kt

@@ -12,8 +12,6 @@ class Outer {
 
             @RequireKotlin("1.3")
             val x = ""
-
-            suspend fun s() {}
         }
     }