g-socthi-mingw.ads, [...]: Remove C_Read and C_Write from internal...

g-socthi-mingw.ads, [...]: Remove C_Read and C_Write from internal implementation unit GNAT.Sockets.Thin...

	* g-socthi-mingw.ads, g-socthi-vms.ads: Remove C_Read and C_Write from
	internal implementation unit GNAT.Sockets.Thin,
	as their usage for sockets is non-portable (using the read and write
	functions from the system runtime library is fine on UNIX but won't
	work under Windows).

	* mingw32.h: Update copyright notice.

From-SVN: r91297