Deprecate SDL_GetRevisionNumber and update things for git instead of hg.

Fixes #4063

build-scripts/update-copyright.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 find . -type f -exec grep -Il "Copyright" {} \;     \
-| grep -v \.hg                             \
+| grep -v \.git                             \
 | while read file;                            \
 do \
   LC_ALL=C sed -b -i "s/\(.*Copyright.*\)[0-9]\{4\}\( *Sam Lantinga\)/\1`date +%Y`\2/" "$file"; \