fix: no contrast issue for lsp popups

Issue was introduced with 2e9b1d4, defining NormalFloat to srcery_bg was
a bad idea and broke other popups, due to lacking background contrast.

I left in the border fix though, so that popup borders match what's
configured for telescope.

This still leaves some plugin borders looking a bit off, especially if
they configure the background to something other than NormalFloat.

Fixes: #115

colors/srcery.vim

@@ -173,7 +173,6 @@ call s:HL('SrceryXgray6', s:xgray6)
 "
 call s:HL('Normal', s:bright_white, g:srcery_bg)
 
-call s:HL('NormalFloat', s:bright_white, g:srcery_bg)
 call s:HL('FloatBorder', s:white, g:srcery_bg)
 
 if v:version >= 700