[jdk21u-dev] RFR: 8320769: Remove ill-adviced "make install" target

[Francesco Andreuzzi]

Backport of JDK-8320769. Almost clean, except for a small conflict in `spec.gmc.in`. The target `make install` is not a recommended way to install the build, and may corrupt the user build environment.

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Commit messages:
 - Backport ebbef629c74dc670adc74a3905a6acf17dbd7200

Changes: https://git.openjdk.org/jdk21u-dev/pull/2008/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2008&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320769
  Stats: 104 lines in 4 files changed: 0 ins; 103 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2008.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2008/head:pull/2008

PR: https://git.openjdk.org/jdk21u-dev/pull/2008