debug: simplify css since top stack frame icon is same for light and dark theme

src/vs/workbench/parts/debug/browser/media/current-and-breakpoint-dark.svg

-<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><g fill="none" fill-rule="evenodd"><g><g transform="translate(1 3)"><path d="M9.188 0H4.375C1.96 0 0 2.24 0 5s1.96 5 4.375 5h5.25L15 5 9.625 0h-.438z" fill="#FFD838"/><circle fill="#c10" cx="5" cy="5" r="3"/></g></g></g></svg>
\ No newline at end of file

src/vs/workbench/parts/debug/browser/media/current-arrow-dark.svg

-<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><g fill="none" fill-rule="evenodd"><g fill="#FFD838"><g><path d="M10.188 3H5.375C2.96 3 1 5.24 1 8s1.96 5 4.375 5h5.25L16 8l-5.375-5h-.438z"/></g></g></g></svg>
\ No newline at end of file

src/vs/workbench/parts/debug/browser/media/debug.contribution.css

@@ -72,7 +72,10 @@
 
 .monaco-editor .debug-top-stack-frame-glyph.debug-breakpoint-glyph,
 .monaco-editor .debug-top-stack-frame-glyph.debug-breakpoint-conditional-glyph,
-.monaco-editor .debug-breakpoint-column.debug-breakpoint-glyph-column.debug-top-stack-frame-column::before {
+.monaco-editor .debug-breakpoint-column.debug-breakpoint-glyph-column.debug-top-stack-frame-column::before,
+.monaco-editor.vs-dark .debug-top-stack-frame-glyph.debug-breakpoint-glyph,
+.monaco-editor.vs-dark .debug-top-stack-frame-glyph.debug-breakpoint-conditional-glyph,
+.monaco-editor.vs-dark .debug-breakpoint-column.debug-breakpoint-glyph-column.debug-top-stack-frame-column::before {
 	background: url('current-and-breakpoint.svg') center center no-repeat;
 }
 
@@ -184,10 +187,6 @@
 	background-color: rgba(255, 255, 0, 0.2)
 }
 
-.monaco-editor.vs-dark .debug-top-stack-frame-column::before {
-	background: url('current-arrow-dark.svg') center center no-repeat;
-}
-
 .monaco-editor.vs-dark .debug-breakpoint-glyph,
 .monaco-editor.vs-dark .debug-breakpoint-column.debug-breakpoint-glyph-column::before {
 	background: url('breakpoint-dark.svg') center center no-repeat;
@@ -213,20 +212,10 @@
 	background: url('breakpoint-unverified-dark.svg') center center no-repeat;
 }
 
-.monaco-editor.vs-dark .debug-top-stack-frame-glyph {
-	background: url('current-arrow-dark.svg') center center no-repeat;
-}
-
 .monaco-editor.vs-dark .debug-focused-stack-frame-glyph {
 	background: url('stackframe-arrow-dark.svg') center center no-repeat;
 }
 
-.monaco-editor.vs-dark .debug-top-stack-frame-glyph.debug-breakpoint-glyph,
-.monaco-editor.vs-dark .debug-top-stack-frame-glyph.debug-breakpoint-conditional-glyph,
-.monaco-editor.vs-dark .debug-breakpoint-column.debug-breakpoint-glyph-column.debug-top-stack-frame-column::before {
-	background: url('current-and-breakpoint-dark.svg') center center no-repeat;
-}
-
 .monaco-editor.vs-dark .debug-focused-stack-frame-glyph.debug-breakpoint-glyph,
 .monaco-editor.vs-dark .debug-focused-stack-frame-glyph.debug-breakpoint-conditional-glyph {
 	background: url('stackframe-and-breakpoint-dark.svg') center center no-repeat;