[clangd] Fix a lit-test.

[kadircet]

Summary

Fixes https://bugs.llvm.org/show_bug.cgi?id=40593.
Non-percent-encoded chars doesn't cause any problems on the input-side since we
assume everything after authority section is data and don't interpret them as
delimeters.

[sammccall]

Hmm, this removes a useful assertion, and still leaves us sending invalid (or at least non-canonical) URIs in the input.
But I don't see a better fix really - lit tests are painful :-(

test/clangd/Inputs/background-index/definition.jsonrpc

"textDocument": {
       "uri": "file://DIRECTORY/bar.cpp"
     },
     "position": {
       "line": 2,
       "character": 8
     }
   }
 }
-# CHECK: "uri": "file://DIRECTORY/foo.cpp"
+# CHECK: "uri": "file://{{.*}}/foo.cpp"
 ---
 {"jsonrpc":"2.0","id":3,"method":"shutdown"}
 ---
 {"jsonrpc":"2.0","method":"exit"}