Clean up unused images (#404)

Dependencies

• [2] GMIKEXTA * Forgot to commit.
• [3] BW6TYQJS Use local copy of the Persona sign in button
• [4] IK53RV4V
• [5] QVSQ4KXF
• [6] A4ZMBK7D * Icon for ISOs.
• [7] D5QIOJGP * Move everything up one directory.
• [8] MFHM3RLC * Add an icon for PDFs.
• [9] YBUGFKLE Use a distinct icon for cancelled builds
• [10] FHF6IZJQ * Basic release management: releases are now dynamically computed as
• [11] JREZM2S2 Add channel as a product type.
• [12] DGVPFNCU * Grabbed a logo. TODO: check copyright status.
• [13] DVNWJXWW * Generic declaration of build products.
• [14] E2ZY5TE5
• [15] 5QE3TIHP hydra: add status icon per jobset on project page
• [16] IZEXRZWT Replace old logo with Nix/NixOS logo.
• [17] N2ZF5JUL Use a different icon for aborted builds
• [18] 44AGCSXK Use a proper spinning wheel icon
• [19] US27ZTX5 * HydraFrontend -> Hydra.
• [20] ELABMHJI * hydra: layout changes
• [21] XZJFZSCJ User color instead of a big animated GIF to indicate whether a build is running
• [22] DAGSOQW3 use newer icons consistently
• [23] 3TL5XENE Different icons (darker red) for cancelled builds. Fixes #25.
• [24] TQKGQ5R3
• [25] ZI535LI6 * hydra: 'new' UI for project/jobset/job/build
• [26] 74VYRQ6W Add an icon for binary distributions

Change contents

• file deletion: arrow-down.gif (----------)
  [4.2196]→[2.103:128](∅→∅),[2.128]→[2.1:1](∅→∅)
• file deletion: failure-some.gif (----------)
  [4.2196]→[4.1727:1754](∅→∅),[4.1754]→[4.1510:1510](∅→∅)
• file deletion: arrow-right-active.gif (----------)arrow-right-active.gif (----------)arrow-right-active.gif (----------)
  [4.1279]→[4.1298:1331](∅→∅),[4.1331]→[4.4906:4906](∅→∅),[4.2196]→[4.2215:2248](∅→∅),[4.2248]→[4.4906:4906](∅→∅),[4.302]→[4.5011:5044](∅→∅),[4.5044]→[4.4906:4906](∅→∅)
• file deletion: arrow-right.gif (----------)arrow-right.gif (----------)arrow-right.gif (----------)
  [4.1279]→[4.1331:1357](∅→∅),[4.1357]→[4.5046:5046](∅→∅),[4.2196]→[4.2248:2274](∅→∅),[4.2274]→[4.5046:5046](∅→∅),[4.302]→[4.5148:5174](∅→∅),[4.5174]→[4.5046:5046](∅→∅)
• file deletion: failure.gif (----------)failure.gif (----------)failure.gif (----------)
  [4.302]→[4.557:579](∅→∅),[4.579]→[4.322:322](∅→∅),[4.1279]→[4.1401:1423](∅→∅),[4.1423]→[4.322:322](∅→∅),[4.2196]→[4.2318:2340](∅→∅),[4.2340]→[4.322:322](∅→∅)
• file deletion: question-mark.png (----------)question-mark.png (----------)
  [4.2196]→[4.2402:2430](∅→∅),[4.2430]→[4.10509:10509](∅→∅),[4.1279]→[4.11097:11125](∅→∅),[4.11125]→[4.10509:10509](∅→∅)
• file deletion: success.gif (----------)success.gif (----------)success.gif (----------)
  [4.302]→[4.747:769](∅→∅),[4.769]→[4.581:581](∅→∅),[4.1279]→[4.1537:1559](∅→∅),[4.1559]→[4.581:581](∅→∅),[4.2196]→[4.2520:2542](∅→∅),[4.2542]→[4.581:581](∅→∅)
• file deletion: persona_sign_in_blue.png (----------)
  [4.2196]→[3.3687:3722](∅→∅),[3.3722]→[3.1:1](∅→∅)
• file deletion: information_128.png (----------)
  [4.2196]→[4.248659:248689](∅→∅),[4.248689]→[4.236166:236166](∅→∅)
• file deletion: information_256.png (----------)
  [4.2196]→[4.279553:279583](∅→∅),[4.279583]→[4.248691:248691](∅→∅)
• file deletion: information_32.png (----------)
  [4.2196]→[4.281457:281486](∅→∅),[4.281486]→[4.279585:279585](∅→∅)
• file deletion: information_64.png (----------)
  [4.2196]→[4.286146:286175](∅→∅),[4.286175]→[4.281488:281488](∅→∅)