Remove Julia v1.8 version check for precompilation

Since the current Julia LTS is v1.10, we can enable precompilation for
all supported Julia versions (1.6+). This removes the version check that
was preventing Julia 1.6 and 1.7 users from benefiting from precompilation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude

src/RootedTrees.jl

@@ -1613,9 +1613,7 @@ function __init__()
     return nothing
 end
 
-# explicit precompilation on Julia v1.8 and newer
-@static if VERSION >= v"1.8"
-    include("precompile.jl")
-end
+# explicit precompilation
+include("precompile.jl")
 
 end # module