Delete obsolete clang prebuilts.

Deleted versions:
- clang-r416183b
- clang-r450784d1
- clang-r458507
- clang-r468909b

Bug: 244341573
Test: presubmit
Change-Id: I5374daefc5b33cf1bb1dce70d4b1602fcf8787f8
Merged-In: I5374daefc5b33cf1bb1dce70d4b1602fcf8787f8
(cherry picked from commit 8937102e9fc9aaa1d34032dbd5ea17bb458158c8)
23118 files changed