after libint2 merge

[loriab]

tasks for after #1721. feel free to add items.

• [ ] switch CI to conda package, not from-source build
• [ ] remove Libint1 & Libint1t
• [ ] remove ERD #1780
• [ ] determine the best way to handle spherical harmonic max AM requirements in libmints, without the LIBINT_MAX_AM macro
• [ ] ~fix lgtm l2 build and move extra cmake out of main CMakeLists.txt~ LGTM defunct
• [ ] resolve libint2_DIR vs. Libint2_DIR with Valeev
• [x] update sphinx<2 requirement -- we're on 7 now?
• [ ] update one electron integrals to use Libint2, and remove existing routines

[JonathonMisiewicz]

Per conference call, L2 is moved to 1.5.