RFR: 8293937: x86: Drop LP64 conditions from clearly x86_32 code

[Aleksey Shipilev]

Noticed this when porting Loom on x86_32. There are `*_x86_32.cpp` files that use `_LP64` as if it matters for them. It does not make sense, as in those files we always have `!_LP64`. We can drop the conditionals and clean the code. 

Proof of completeness:


$ ack LP64 src/hotspot/ | grep _32
src/hotspot/cpu/x86/register_x86.hpp:386:                          NOT_LP64( 8 + ) // FILL0-FILL7 in x86_32.ad
src/hotspot/cpu/x86/vm_version_x86.hpp:733:    return LP64_ONLY(true) NOT_LP64(false); // not implemented on x86_32

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/10305/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10305&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293937
  Stats: 46 lines in 2 files changed: 0 ins; 37 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/10305.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10305/head:pull/10305

PR: https://git.openjdk.org/jdk/pull/10305