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/app/internal/gpu/caches.go

@@ -81,7 +81,7 @@ func (r *opCache) get(key ops.Key) (resource, bool) {
 
 func (r *opCache) put(key ops.Key, val resource) {
 	if _, exists := r.newRes[key]; exists {
-		panic(fmt.Errorf("key exists, %p", key))
+		panic(fmt.Errorf("key exists, %#v", key))
 	}
 	r.res[key] = val
 	r.newRes[key] = val

ui/app/internal/gpu/gpu.go

@@ -349,7 +349,7 @@ func (g *GPU) renderLoop(glctx gl.Context) error {
 					zt, st, covt, cleant := zopsTimer.Elapsed, stencilTimer.Elapsed, coverTimer.Elapsed, cleanupTimer.Elapsed
 					ft := zt + st + covt + cleant
 					q := 100 * time.Microsecond
-					zt, st, covt, cleant = zt.Round(q), st.Round(q), covt.Round(q), cleant.Round(q)
+					zt, st, covt = zt.Round(q), st.Round(q), covt.Round(q)
 					ft = ft.Round(q)
 					res.summary = fmt.Sprintf("f:%7s zt:%7s st:%7s cov:%7s", ft, zt, st, covt)
 				}