optimize/clean up a few of the table changes (#11076)

# Description

@sholderbach pointed out some places that I could help improve the code
in the table command changes. This PR tries to implement those.

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crates/nu-table/src/common.rs

@@ -182,7 +182,6 @@ pub fn load_theme(mode: TableMode) -> TableTheme {
         TableMode::Compact => TableTheme::compact(),
         TableMode::WithLove => TableTheme::with_love(),
         TableMode::CompactDouble => TableTheme::compact_double(),
-        TableMode::Default => TableTheme::rounded(),
         TableMode::Rounded => TableTheme::rounded(),
         TableMode::Reinforced => TableTheme::reinforced(),
         TableMode::Heavy => TableTheme::heavy(),