remove outdated opensslVersion from build.gradle

[brody4hire]

git grep shows the outdated opensslVersion used in only one place, looks safe to remove

(I am actually trying to build an updated version in my workarea, with Android NDK r23 which seems to be their latest LTS, as I make this PR)

While I don't anticipate this to break anything, I am raising this as a draft PR NOT TESTED until I get a chance to test this from start to finish. In case a maintainer feels confident to apply this proposal now WITH AN UPDATED TITLE, that would be awesome as well.

And thanks to @developernotes for updating SQLCIPHER_ANDROID_VERSION in the documentation.

[brody4hire]

I have rebased this update and tested building (tested building with Android NDK r23, with -fuse-ld=bfd removed to succeed with NDK r23), would appreciate a review ... thanks.

[developernotes]

Hi @brodybits

That is correct, the opensslVersion referenced in the Gradle file is an artifact from the library when it directly bundled an OpenSSL source package. Now that you must externally provide an OpenSSL source tree, that variable is no longer necessary. Thanks!