Cleaned up .gitignore, removing autotools files

This also removes various names for build directories. We're not going to add everyone's random build directory name, if you want git to appear clean you can build in the build subdirectory or out of tree.

.gitignore

@@ -1,20 +1,5 @@
-aclocal.m4
-autom4te*
-config.cache
-config.log
-config.status
-libtool
-Makefile
-Makefile.rules
-sdl3-config
-sdl3-config.cmake
-sdl3-config-version.cmake
-sdl3.pc
-SDL3.spec
-build
-gen
-Build
-buildbot
+build/
+buildbot/
 /VERSION.txt
 __pycache__
 
@@ -168,13 +153,3 @@ test/testvulkan
 test/testwm2
 test/testyuv
 test/torturethread
-
-builddir/
-!build-scripts/
-debian/*.debhelper.log
-debian/*.substvars
-debian/*.tar.gz
-debian/.debhelper/
-debian/files
-debian/libsdl*/
-debian/tmp/