base: Remove unnecessary entries in .gitignore

[norihiro]

Description

Removes the entries for generated files from .gitignore file.

Motivation and Context

the commit 21886adb3 moves the destination of the generated files into the build directory so that it is unnecessary to hide the generated files by .gitignore. By removing these entries, it's easier to find the unnecessary files by git status command.

How Has This Been Tested?

Tested OS(s): Fedora 36

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• [x] I have read the Contributing Guidelines.
• [ ] All commit messages are properly formatted and commits squashed where appropriate.
• [x] My code is not on master or a release/* branch.
• [x] The code has been tested.
• [x] I have included updates to all appropriate documentation.

[norihiro]

I followed the history and put the prefix base: to the commit title. Let me know if it's wrong.