TEZ-4532: Remove KEYS file from git repo and source distribution

[zabetak]

Projects must publish a KEYS file in their distribution directory which contains all public keys used to sign artifacts (i.e., https://dist.apache.org/repos/dist/release/tez/KEYS).

The KEYS file here is not serving any purpose since it shouldn't be used to verify releases. It adds maintenance overhead (assuming that is kept in sync) and possible confusion to the users with respect to which file they should use to validate the artifacts.

[tez-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	25m 52s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+0 🆗	shelldocs	0m 0s	Shelldocs was not available.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
		_ master Compile Tests _
		_ Patch Compile Tests _
+1 💚	shellcheck	0m 0s	There were no new shellcheck issues.
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
		_ Other Tests _
+1 💚	asflicense	1m 23s	The patch does not generate ASF License warnings.
		28m 6s

Subsystem	Report/Notes
Docker	ClientAPI=1.44 ServerAPI=1.44 base: https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-329/1/artifact/out/Dockerfile
GITHUB PR	#329
JIRA Issue	TEZ-4532
Optional Tests	dupname asflicense shellcheck shelldocs
uname	Linux f39abfe0f548 5.15.0-88-generic #98-Ubuntu SMP Mon Oct 2 15:18:56 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	personality/tez.sh
git revision	master / d8dda5c
Max. process+thread count	51 (vs. ulimit of 5500)
modules	C: . U: .
Console output	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-329/1/console
versions	git=2.34.1 maven=3.6.3 shellcheck=0.7.1
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[ayushtkn]

LGTM