Replace highly vendor-specific icon for PDF with existing platform and vendor neutral icon from vscode-codicons

[petervwyatt]

For PDF, replace the highly vendor-specific product icon (Adobe Acrobat's "cursive A" = https://github.com/jesseweed/seti-ui/blob/master/icons/pdf.svg) with the fully vendor- and platform-neutral vscode-codicons PDF SVG icon from https://github.com/microsoft/vscode-codicons/blob/main/src/icons/file-pdf.svg.

PDF has not been controlled by Adobe since 2008 when ISO published the ISO 32000-1:2008 international standard.

[orta]

Yeah, seems pretty reasonable to me 👍🏻