Stop setting bg in colorscheme

This caused the opposite of what I wanted.

See https://vi.stackexchange.com/questions/12104/what-does-set-background-dark-do

colors/wombat_classic.vim

@@ -1,5 +1,4 @@
 " You probably always want to set this in your vim file
-set background=dark
 let g:colors_name='wombat_classic'
 
 " By setting our module to nil, we clear lua's cache,

colors/wombat_lush.vim

@@ -1,5 +1,4 @@
 " You probably always want to set this in your vim file
-set background=dark
 let g:colors_name='wombat_lush'
 
 " By setting our module to nil, we clear lua's cache,