RFR: 8281459: WebKit 613.1 build broken on M1

[Ambarish Rapte]

This seems like a bad merge issue. 
There were duplicate copies of four methods in `MacroAssemblerARM64.h` which caused WebKit build failure on Mac M1 machines.
Just removing the methods removes the error. 
With the changes in this PR, now the file `MacroAssemblerARM64.h` matches with the WebKit mainline.

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Commit messages:
 - MacOS M1 arch64 build error

Changes: https://git.openjdk.java.net/jfx/pull/730/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=730&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281459
  Stats: 20 lines in 1 file changed: 0 ins; 20 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/730.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/730/head:pull/730

PR: https://git.openjdk.java.net/jfx/pull/730