chore: remove css file about nprogress (#2275)

src/client/theme-default/styles/lib-override/nprogress.css

@@ -1,12 +0,0 @@
-#nprogress .bar {
-  background: var(--vp-c-brand);
-}
-
-#nprogress .spinner-icon {
-  border-top-color: var(--vp-c-brand);
-  border-left-color: var(--vp-c-brand);
-}
-
-#nprogress .peg {
-  box-shadow: 0 0 10px var(--vp-c-brand), 0 0 5px var(--vp-c-brand);
-}