RFR: 4890041: Remove TAB and Shift TAB from Popup Menu in Motif Look & Feel

[Prasanta Sadhukhan]

This is a cleanup of unneeded TAB and Shift TAB keybindings for PopupMenu.selectedWindowInputMapBindings which is consistent with other L&Fs as can be seen here

https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicLookAndFeel.java#L1131

https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/synth/SynthLookAndFeel.java#L702

https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/com/sun/java/swing/plaf/gtk/GTKLookAndFeel.java#L806

No regression test added for this code cleanup

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Commit messages:
 - 4890041: Remove TAB and Shift TAB from Popup Menu in Motif Look & Feel

Changes: https://git.openjdk.org/jdk/pull/9609/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9609&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-4890041
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9609.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9609/head:pull/9609

PR: https://git.openjdk.org/jdk/pull/9609