package/qt5webview: drop qt 5.6 support

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 55e5b3464b212dd729b25e5f89f692958b4e4a26)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qt5/qt5webview/qt5webview.hash

@@ -1,6 +1,3 @@
-# Hash from: https://download.qt.io/archive/qt/5.6/5.6.3/submodules/qtwebview-opensource-src-5.6.3.tar.xz.sha256
-sha256 768a456e89f0fd7cbf39ac6b282e078a098e7426651c0b3d453b10c5c44bd81c qtwebview-opensource-src-5.6.3.tar.xz
-
 # Hash from: https://download.qt.io/official_releases/qt/5.12/5.12.8/submodules/qtwebview-everywhere-src-5.12.8.tar.xz.sha256
 sha256  f6492f01c3c0b2b44ffdd9e7d55d11d39e960ea0080cd29555d0a1be43366de4  qtwebview-everywhere-src-5.12.8.tar.xz