tools: gitignore: Fix tools/generated path

'git status' shows 'tools/generated/' after running the build, which is
wrong. The corresponding .gitignore rule was already added in commit
c623642d ("Adjust gitignore for tools/generated/"), but because of
superfluous 'tools/' part it wasn't in effect. Remove incorrect 'tools/'
part to fix it.

While at it, remove tools/ path incorrectly added to the top-level
.gitignore in commit 801c4822 (".gitignore: ignore misc include,
simple-bin, and tools/generated build artifacts"), as it's required in
the comment on the top of .gitignore:

    # NOTE! Don't add files that are generated in specific
    # subdirectories here. Add them in the ".gitignore" file
    # in that subdirectory instead.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Fixes: c623642d ("Adjust gitignore for tools/generated/")
Fixes: 801c4822 (".gitignore: ignore misc include, simple-bin, and tools/generated build artifacts")