gitignore: Simplify top-level gitignore file.

All build artefacts are now placed in build*/ directories so there's no
longer any need to hide files like .o with .gitignore.

Signed-off-by: Damien George <damien@micropython.org>

.gitignore

@@ -1,48 +1,17 @@
-# Compiled Sources
-###################
-*.o
-*.a
-*.elf
-*.bin
-*.map
-*.hex
-*.dis
-*.exe
-
-# Packages
-############
-
-# Logs and Databases
-######################
-*.log
-
-# VIM Swap Files
-######################
-*.swp
-
 # Build directories
-######################
 build/
 build-*/
+docs/genrst/
 
 # Test failure outputs
-######################
 tests/results/*
 
 # Python cache files
-######################
 __pycache__/
-*.pyc
 
 # Customized Makefile/project overrides
-######################
 GNUmakefile
 user.props
 
-# Generated rst files
-######################
-genrst/
-
 # MacOS desktop metadata files
-######################
 .DS_Store