Remove certain lines (with ---- and empty lines) from txt file using readLines() or read_lines()

Question

I have this text file called textdata.txt:

TREATMENT DATA

------------------------------------
A: Text1
B: Text2

C: Text3
D: Text4

E: Text5
F: Text6
G: Text7

I would like to remove the whole line with --------- and the empty lines using readLines or read_lines:

When I use readLines("textdata.txt") I get:

 [1] "TREATMENT DATA"                      
 [2] ""                                    
 [3] "------------------------------------"
 [4] "A: Text1"                            
 [5] "B: Text2"                            
 [6] ""                                    
 [7] "C: Text3"                            
 [8] "D: Text4"                            
 [9] ""                                    
[10] "E: Text5"                            
[11] "F: Text6"                            
[12] "G: Text7"  

I would like to have, expected output:

 [1] "TREATMENT DATA"                      
 [2] "A: Text1"                            
 [3] "B: Text2"                                                               
 [4] "C: Text3"                            
 [5] "D: Text4"                                                             
 [6] "E: Text5"                            
 [7] "F: Text6"                            
 [8] "G: Text7"                                                             

Background: I have de facto no experience handling files with R. The basic idea is to get a .txt format from which I can load multiple text files stored in a folder to one dataframe.