package/qt5webview: drop qt 5.6 support

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/5.12/5.12.7/submodules/qtwebview-everywhere-src-5.12.7.tar.xz.sha256
 sha256 d3f82d2ceab59dc4dee3b6f54f4b70869c199d63f4534b299d900cdacc9b7be7 qtwebview-everywhere-src-5.12.7.tar.xz