Remove generated e3.cfg

[jeonghanlee]

When we install e3 and move them other path, or mount it with the different directory path name. We cannot source "setE3Env.bash" properly, because of the generated e3.cfg.

After the installation, we know exactly where setE3Env.bash is, so we might guess, where is. So we can use them in order to identify EPICS_BASE, REQUIRE, and REQUIRE_VERSION.

[jeonghanlee]

implemented at 58bef31 . Once require is installed, setE3Env.bash can extract the EPICS BASE base on the installation path instead of a generated file. By this, the different mount path is also OK.