Update postgresql-client, postgresql-server-dev and libpq to PG12 (#151)

This undoes the pinning of libpq added in #148 and additionally updates
`postgresql-client` and `postgresql-server-dev` to the PG12 releases,
to support Heroku Postgres 12.

Since #148 the upstream Postgres project has improved the libpq 12 error
handling, such that it now provides a clearer error message when the
validation of connection parameters fail, which makes it easier for
customers to identify that it's due to their app having an invalid
configuration.

The build scripts for Cedar-14 have not been modified since the upstream
Postgres project has not released PG12 versions of the packages for
Ubuntu-14 given it is EOL.

Release notes:
https://www.postgresql.org/docs/12/release-12.html

Refs W-7113082.
Closes #147.

heroku-16-build/bin/heroku-16-build.sh

@@ -71,7 +71,7 @@ apt-get install -y --force-yes \
     libyaml-dev \
     libzip-dev \
     mercurial \
-    postgresql-server-dev-11 \
+    postgresql-server-dev-12 \
     python-dev \
     ruby-dev \
     zlib1g-dev \

heroku-16-build/installed-packages.txt

@@ -541,10 +541,10 @@ pgdg-keyring
 pinentry-curses
 pkg-config
 poppler-data
-postgresql-client-11
+postgresql-client-12
 postgresql-client-common
 postgresql-common
-postgresql-server-dev-11
+postgresql-server-dev-12
 procps
 python
 python-bzrlib

heroku-16/bin/heroku-16.sh

@@ -9,17 +9,7 @@ deb http://archive.ubuntu.com/ubuntu/ xenial main universe
 deb http://archive.ubuntu.com/ubuntu/ xenial-security main universe
 deb http://archive.ubuntu.com/ubuntu/ xenial-updates main universe
 
-# Use the PG11 version of libpq to work around:
-# https://github.com/heroku/stack-images/issues/147
-# We have to specify both 'main' and '11' since the latter only contains a subset of the packages.
-deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main 11
-EOF
-
-# Give priority to the PG11 version of libpq, rather than main's PG12.
-cat >/etc/apt/preferences.d/pgdg.pref <<EOF
-Package: *
-Pin: release o=apt.postgresql.org,c=11
-Pin-Priority: 600
+deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main
 EOF
 
 apt-key add - <<'PGDG_ACCC4CF8'
@@ -146,7 +136,7 @@ apt-get install -y --force-yes \
     netcat-openbsd \
     openssh-client \
     openssh-server \
-    postgresql-client-11 \
+    postgresql-client-12 \
     python \
     ruby \
     socat \

heroku-16/installed-packages.txt

@@ -312,7 +312,7 @@ perl-base
 perl-modules-5.22
 pgdg-keyring
 poppler-data
-postgresql-client-11
+postgresql-client-12
 postgresql-client-common
 procps
 python

heroku-18-build/bin/heroku-18-build.sh

@@ -74,7 +74,7 @@ apt-get install -y --force-yes --no-install-recommends \
     libyaml-dev \
     libzip-dev \
     mercurial \
-    postgresql-server-dev-11 \
+    postgresql-server-dev-12 \
     python-dev \
     ruby-dev \
     zlib1g-dev \

heroku-18-build/installed-packages.txt

@@ -510,10 +510,10 @@ pgdg-keyring
 pinentry-curses
 pkg-config
 poppler-data
-postgresql-client-11
+postgresql-client-12
 postgresql-client-common
 postgresql-common
-postgresql-server-dev-11
+postgresql-server-dev-12
 procps
 python
 python-bzrlib

heroku-18/bin/heroku-18.sh

@@ -13,18 +13,8 @@ EOF
 apt-get update
 apt-get install -y --no-install-recommends gnupg
 
-# Use the PG11 version of libpq to work around:
-# https://github.com/heroku/stack-images/issues/147
-# We have to specify both 'main' and '11' since the latter only contains a subset of the packages.
 cat >>/etc/apt/sources.list <<EOF
-deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main 11
-EOF
-
-# Give priority to the PG11 version of libpq, rather than main's PG12.
-cat >/etc/apt/preferences.d/pgdg.pref <<EOF
-Package: *
-Pin: release o=apt.postgresql.org,c=11
-Pin-Priority: 600
+deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main
 EOF
 
 apt-key add - <<'PGDG_ACCC4CF8'
@@ -180,7 +170,7 @@ apt-get install -y --no-install-recommends \
     openssh-client \
     openssh-server \
     patch \
-    postgresql-client-11 \
+    postgresql-client-12 \
     python \
     rename \
     rsync \

heroku-18/installed-packages.txt

@@ -306,7 +306,7 @@ perl-modules-5.26
 pgdg-keyring
 pinentry-curses
 poppler-data
-postgresql-client-11
+postgresql-client-12
 postgresql-client-common
 procps
 python