compiletest: remove useless env gates from spec_constant-attr

Author: Firestar99

tests/compiletests/ui/dis/spec_constant-attr.rs

@@ -9,11 +9,6 @@
 // normalize-stderr-test "OpExtension .SPV_KHR_vulkan_memory_model.\n" -> ""
 // normalize-stderr-test "OpMemoryModel Logical Vulkan" -> "OpMemoryModel Logical Simple"
 
-// FIXME(eddyb) this should use revisions to track both the `vulkan1.2` output
-// and the pre-`vulkan1.2` output, but per-revisions `{only,ignore}-*` directives
-// are not supported in `compiletest-rs`.
-// ignore-vulkan1.2
-
 use spirv_std::spirv;
 
 #[spirv(fragment)]