Remove dlltool prefix hack

[glandium]

#1967 added a dlltool option (-t) to make the *_gnu import library member names more consistent across different versions of binutils. That required a sort of a hack to use a different prefix based on what the library name looked like, because of inconsistencies in the win32metadata. Those have since been fixed, so the hack can now be removed, which essentially looks like this:

diff --git a/crates/tools/gnu/src/main.rs b/crates/tools/gnu/src/main.rs
index aef4b96f9..e4bb99aba 100644
--- a/crates/tools/gnu/src/main.rs
+++ b/crates/tools/gnu/src/main.rs
@@ -109,11 +109,7 @@ EXPORTS
         });
         // Ensure consistency in the prefixes used by dlltool.
         cmd.arg("-t");
-        if library.contains('.') {
-            cmd.arg(format!("{}_", library).replace('.', "_").replace('-', "_"));
-        } else {
-            cmd.arg(format!("{}_dll_", library).replace('-', "_"));
-        }
+        cmd.arg(format!("{}_", library).replace('.', "_").replace('-', "_"));
     }
     cmd.output().unwrap();
 

Unfortunately, as is, this also generates different import libraries than what's in the repo because of what's now fixed in microsoft/win32metadata#1247.
So once there's a new metadata release and it's pulled in here, the above patch can be applied.

[kennykerr]

I believe this can now be fixed since #2050 has arrived.