Remove 128bit code generation from test case

128 bit integer support is not always available for every GCC arch and we
will need to rely on runtime libraries for these operations in the future.

Addresses #1439

gcc/testsuite/rust/compile/torture/issue-1432.rs

@@ -67,6 +67,5 @@ impl_uint!(
     u16 = "u16",
     u32 = "u32",
     u64 = "u64",
-    u128 = "u128",
     usize = "usize"
 );