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/egl.go

@@ -89,7 +89,7 @@ func (c *context) Present() error {
 		c.srgbFBO.Blit()
 	}
 	if !eglSwapBuffers(c.eglCtx.disp, c.eglSurf) {
-		return fmt.Errorf("eglSwapBuffers failed (%x%x)", eglGetError())
+		return fmt.Errorf("eglSwapBuffers failed (%x)", eglGetError())
 	}
 	if c.srgbFBO != nil {
 		c.srgbFBO.AfterPresent()