Compiler Attributes: fix comment concerning GCC 4.6

GCC 4.6 is not supported anymore, so remove a reference to it,
leaving just the part about version prior GCC 5.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

include/linux/compiler_attributes.h

@@ -22,7 +22,7 @@
 
 /*
  * __has_attribute is supported on gcc >= 5, clang >= 2.9 and icc >= 17.
- * In the meantime, to support 4.6 <= gcc < 5, we implement __has_attribute
+ * In the meantime, to support gcc < 5, we implement __has_attribute
  * by hand.
  */
 #ifndef __has_attribute