[DOC] man: Remove environment variable RUBY_GC_HEAP_INIT_SLOTS

man/ruby.1

@@ -566,10 +566,7 @@ Reaching the old malloc limit.
 .Pp
 There are currently 4 possible areas where the GC may be tuned by
 the following environment variables:
-.Bl -hang -compact -width "RUBY_GC_HEAP_INIT_SLOTS"
-.It Ev RUBY_GC_HEAP_INIT_SLOTS
-Initial allocation slots. Applies to all slot sizes.  Introduced in Ruby 2.1, default: 10000.
-.Pp
+.Bl -hang -compact -width "RUBY_GC_HEAP_%d_INIT_SLOTS"
 .It Ev RUBY_GC_HEAP_ Ns Ar %d Ns Ev _INIT_SLOTS
 Initial allocation of slots in a specific heap.
 The available heaps can be found in the keys of `GC.stat_heap`.