bindings-GLFW.cabal: drop non-existent files glfw/src/x11_gamma.c and glfw/src/x11_unicode.c
bindings-GLFW.cabal: drop non-existent files glfw/src/x11_gamma.c and glfw/src/x11_unicode.c

Peaker/bindings-GLFW,bsl/bindings-GLFW,sgraf812/bindings-GLFW,da-x/bindings-GLFW