Remove unused helper script 'extract_file.py'

The code from this script seems to be part of
bldinstallercommon.py now.

Change-Id: I6dc7b30b5917d14cc10cf1ac427bfc88ad0b328b
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
mkqt5bld: Split patch_android_prl_files function in two

Split part of the code that doesn't patch android prl files into
rename_android_soname_files(), which is really what that part of
the code is doing.

Change-Id: I25470dcee2337890ae198e63b326b82e8535ebda
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>