floss: removing googletest manual build steps

* googletest packages (libgtest-dev and libgmock-dev) have pkg-config
  files now. So, the build and installation steps are no longer
  required.

* Here are the installation information about these packages:
  $ $ apt list --installed libgtest-dev libgmock-dev
  Listing... Done
  libgmock-dev/glinux-rodete-base-20220316.03.07,now 1.11.0-3 amd64
  [installed]
  libgtest-dev/glinux-rodete-base-20220316.03.07,now 1.11.0-3 amd64
  [installed]

  $dpkg -L libgtest-dev | grep gtest.pc
  /usr/lib/x86_64-linux-gnu/pkgconfig/gtest.pc

  $ dpkg -L libgmock-dev | grep gmock.pc
  /usr/lib/x86_64-linux-gnu/pkgconfig/gmock.pc

* Adding libabsl-dev package as it's required by libchrome.

Bug: 227287284
Tag: #floss
Test: ./biuld.py --target docs and ./build.py
Change-Id: I46c9f16ce328041c8953c5ad2b513719997fb096