internal/mod/modload: remove debugging panic with sprintf

I introduced this code two days ago in https://cuelang.org/cl/1195701
and while developing, I had used Sprintf to inspect error values
and panic to loudly surface when they happened in our test suite.

Unfortunately, I forgot the panic and it made it past code review too.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I881d2e6ca2979470d7253b2bab0625644829975e
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1195847
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Rustam Abdullaev <rustam@cue.works>

internal/mod/modload/tidy.go

@@ -181,8 +181,6 @@ func (ld *loader) resolveDependencies(ctx context.Context, rootPkgPaths []string
 				if errors.As(err, &missingErr) {
 					err = &ErrModuleNotTidy{Reason: fmt.Sprintf(
 						"missing dependency providing package %s", missingErr.Path)}
-				} else {
-					panic(fmt.Sprintf("%#v\n", err) + ": " + err.Error())
 				}
 				return nil, nil, err
 			}