all: fix some issues spotted by static analysis

First, vet was upset by two incorrect fmt verbs. One was an extra %x,
when there was just one argument, so remove it. Another was a %p with a
non-pointer. It's a struct, so for now simply use %#v.

Second, staticcheck found some unused or unnecessary bits of code;
remove the obvious ones.

Finally, staticcheck also complained about some error strings which were
capitalized or had periods. Adjust those, which also makes all error
messages more consistent.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

ui/internal/ops/reader.go

@@ -33,7 +33,6 @@ type Key struct {
 
 // Shadow of ui.MacroOp.
 type macroOp struct {
-	recording bool
 	ops       *ui.Ops
 	version   int
 	pc        pc