RFR: JDK-8275856: Remove MetaspaceHandleDeallocations debug switch

[Thomas Stuefe]

`MetaspaceHandleDeallocations` can be used to switch off deallocation handling (which takes care of reusing prematurely deallocated metaspace blocks in case of e.g. class redefinitions or class loading errors). Technically this is a leak then, the intent was to switch off the deallocation handling for error analysis. 

It had been very rarely used, only in the first stages of JEP 387, and it is not covered by tests. I propose to remove it to reduce code complexity.

Tests: GHAs, manual tests (note that we have regression tests in place for deallocation handling), SAP nightlies

-------------

Commit messages:
 - remove MetaspaceHandleDeallocations switch

Changes: https://git.openjdk.java.net/jdk/pull/6098/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6098&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275856
  Stats: 69 lines in 5 files changed: 9 ins; 40 del; 20 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6098.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6098/head:pull/6098

PR: https://git.openjdk.java.net/jdk/pull/6098